Hip replacement navigation system and method

ABSTRACT

In another embodiment, a hip joint navigation jig is provided that includes an anatomical interface comprising a bone engagement portion. A registration jig is also provided that is coupled, e.g., removeably, with the anatomical interface. A rotatable member is provided for rotation about an axis that is not vertical when the jig is mounted to the bone adjacent to a hip joint and the registration jig is coupled with the anatomical interface. An anatomy engaging probe is coupled with the rotatable member for rotation about the axis and is translatable to enable the probe to be brought into contact with a plurality of anatomical landmarks during a procedure. An inertial sensor is coupled with the probe to indicate orientation related to the landmarks, the sensor being disposed in a different orientation relative to horizontal when the probe is in contact with the landmarks.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/800,620, filed Mar. 13, 2013, which claims priority under 35U.S.C. § 119(e) to U.S. Provisional Application No. 61/683,167 filed onAug. 14, 2012 and U.S. Provisional Application No. 61/761,617 filed onFeb. 6, 2013. Any and all applications for which a foreign or domesticpriority claim is identified in the Application Data Sheet as filed withthe present application including U.S. patent application Ser. No.13/800,620 filed Mar. 13, 2013, U.S. provisional application No.61/683,167, filed Aug. 14, 2012, and U.S. provisional application No.61/761,617, filed Feb. 6, 2013, are hereby incorporated by referenceunder 37 CFR 1.57.

BACKGROUND OF THE INVENTION Field of the Invention

This application is directed to the field of hip replacement, andparticularly to surgical tools and methods for guiding the preparationof the bones in connection therewith.

Description of the Related Art

Hip replacement surgery is common and getting more common by the year.One persistent issue with hip replacement is the relatively highincidence of poor placement of the cup and ball components of theprosthetic hip joint. For example, the cup is optimally placed in aspecific alignment with a plane including a rim of the acetabulum of thepelvis. For several reasons an unacceptably high percentage of patientshave the cup of the artificial hip joint out of alignment with thisplane.

Unfortunately, misalignment can lead to dislocation of the hip as soonas within one year of the implantation procedure. This is particularlyproblematic because recovery from a hip procedure can take many months.Patients undergoing a revision so soon after the initial implantationwill certainly be dissatisfied with their care, being subject toaddition redundant surgery. Of course, all surgery carries some degreeof risk. These poor outcomes are unsatisfactory for patients andsurgeons and are inefficient for the healthcare system as a whole.

Also, in cup placement in total hip arthroplasty, the inclination andanteversion angles are with respect to the Anterior Pelvic Plane(defined as a plane created by the two anterior superior iliac spines(ASIS) and the pubic symphysis). While these anatomical features arevisible/palpable while the patient is in a supine position, the majorityof total hip replacements are accomplished via a posterolateral approachwith the patient in some variation of a lateral position, in which mostof these landmarks are not accessible or visible. Historically,navigation for posterior approach hip replacement has been accomplishedby registering the anatomical features of the Anterior Pelvic Plane withthe patient first in a supine position and, once this plane is recordedby the navigation computer, moving the patient to a lateral position inorder to perform hip surgery—with navigation performed with respect tothe directly registered Anterior Pelvic Plane. This approach to hipnavigation is sub-optimal for surgical workflow because the extramovement of the patient from supine to lateral position takes moresurgeon and staff time and requires breaking sterility and re-draping.This is one of the key reasons why hip navigation has failed to beadopted by most of the market.

Additionally, altered leg length is a common patient complaint arisingfrom hip replacement surgery and has been a common cause of medicalmalpractice lawsuits that arise from hip replacement. Because part ofthe hip replacement procedure requires precise measurements of patientleg length and joint off-set that are frequently difficult to visualizeutilizing conventional instrumentation, there are opportunities toimprove the surgeon's performance of these measurements using computertechnology.

SUMMARY OF THE INVENTION

There is a need for improved systems and methods for providing forproper alignment of hip components with a patient's anatomy during a hipreplacement procedure. This can involve techniques for locating one ormore anatomical landmarks, e.g., discrete anatomy and/or planesincluding multiple points. This can involve techniques for confirmingalignment of a prosthetic component with an anatomical landmark.

In one embodiment, a method is provided for navigating a hip jointreplacement procedure. The method includes advancing a first portion ofa jig into a portion of the pelvis. The portion of the pelvis is ananatomical landmark in some techniques. In others it is not. At leastone inertial sensor is coupled to the jig. The second portion of the jigis moved relative to the first portion to touch, e.g., sequentially, aplurality of anatomical landmarks. This can include touching two orthree landmarks, for example. A cup portion of a replacement joint isplaced in the acetabulum by reference to a plane calculated based ondata from the at least one of a plurality of inertial sensors.

In another embodiment, a hip joint navigation system is provided. Thesystem includes a jig, a first inertial navigation device and a secondinertial navigation device. The jig has an anchor portion adapted to beplaced on the hip, e.g., at an anatomical landmark. The jig also has alandmark acquisition probe coupled with the anchor portion. The probe ismoveable in at least three degrees of freedom. The first inertialnavigation device is configured to be fixed to a pelvis of a patient totrack movements of the pelvis. The first inertial navigation device canbe immovably connected to the pelvis. The second inertial navigationdevice is coupled with the landmark acquisition probe. The landmarkacquisition probe can be moved to touch a plurality of landmarks. Theinertial navigation devices determine the orientation of a plane of theacetabulum based at least in part on the position of the anatomicallandmarks.

In another embodiment, a method of navigating a hip replacementprocedure is provided. A first hip of a patient is positioned on asurgical table and a second hip is positioned off of the table such thatthe anterior pelvic plane is disposed upright (e.g., vertically). A jigis coupled with a bone adjacent to a second hip joint. The jig has amoveable orientation guide. An inertial sensor is coupled with theorientation guide. The orientation guide can be an arm of a registrationprobe in some embodiments. The orientation guide is oriented in a planesubstantially parallel to the plane of the table. The orientation of theinertial sensor is recorded as an indication of the orientation of theanterior pelvic plane. If the anterior pelvic plane is vertical theinertial sensor can indicate the plane of the table, which isperpendicular to the anterior pelvic plane. A cup of an artificial hipjoint is placed in the acetabulum with reference to the orientation ofthe anterior pelvic plane based on the orientation of the inertialsensor.

In another embodiment, a system for determining orientation data inconnection with a hip joint procedure is provided. The system includes adata capture module, a computational module, and a user interfacemodule. The data capture module is configured to receive inertial datafrom an inertial sensor. The computational module is configured toprovide, based on the inertial data, one or more angles of a proxyacetabular plane relative to an anterior pelvic plane. The userinterface module is configured to output a user interface configured tocommunicate orientation data to a user. One or more of these modules isimplemented by one or more processors.

In another embodiment, a method of navigating a hip replacementprocedure is provided. A patient is positioned for posterior orposterolateral approach. A jig is coupled with a bone adjacent to a hipjoint. The jig comprising a landmark acquisition probe having aninertial sensor coupled therewith. Patient condition can be assessed,and based on the patient condition, a selection can be made between afirst plurality of landmarks and a second set of landmarks. The firstset of landmarks can be disposed on an acetabular rim. The plurality oflandmarks can be disposed off of an acetabular rim. The orientation ofthe inertial sensor can be recorded when the landmark acquisition probeis in contact with each of the points of the selected plurality. A cupof an artificial hip joint is positioned in the acetabulum withreference to the recorded orientation to the selected plurality ofpoints.

In another approach, a method of navigating a procedure on a hip jointis provided. At least one aspect of the hip joint is characterizedpre-operatively. A patient is positioned for posterior or posterolateralapproach. A jig is coupled with a bone adjacent to the hip joint (e.g.,part of the pelvis). The jig has a landmark acquisition probe having aninertial sensor coupled therewith. The orientation of the inertialsensor is recorded when the landmark acquisition probe is in contactwith each of a plurality of landmarks. A cup of an artificial hip jointis positioned in the acetabulum with reference to recorded orientationand to estimations of at least one of anteversion and inclinationangles. Estimations of these angles can be based upon thepre-operatively recorded characterization of the hip joint. The recordedorientation can be that of the inertial sensor when the probe is incontact with each of the landmarks.

In another embodiment, a method of navigating a hip replacementprocedure is provided. The method includes positioning a patient forposterior or posterolateral approach. A jig is coupled with anacetabular socket of the patient, the jig having an engagement surfaceformed to closely mate to acetabular bone contours of the specificpatient. The jig comprising a registration feature configured to be in apre-determined orientation relative to the anterior pelvic plane of thepatient when the jig is so-coupled. An inertial sensor is coupled withthe registration feature such that the inertial sensor generates asignal indicating at least one angle relative to the anterior pelvicplane. A prosthetic cup is placed based on the signal.

In another embodiment, a patient specific jig system for hip replacementis provided. The jig system includes an engagement surface and aregistration feature. The engagement surface is formed to closely mateto acetabular bone contours of a specific patient. The registrationfeature is configured to be in a pre-determined orientation relative tothe anterior pelvic plane of the patient when the jig is coupled toclosely mate to acetabular bone contours of the specific patient.

In another embodiment, a method of replacing a hip joint is provided.The method includes coupling a trackable member with a limb forming apart of a hip joint of the patient. The limb is moved to at least fourpoints disposed away from a neutral position of the hip. The four pointsinclude at least one medial extent, at least one lateral extent, atleast one anterior extent, and at least one posterior extent of apatient's range of motion. During the moving step, data is collectedfrom the trackable member indicating the displacement from the neutralposition to each of the extents. A socked component of the prosthetichip joint is placed within the acetabulum. A stem of a femoral componentof a prosthetic hip joint is placed into a proximal femur. A ball of thefemoral component is placed in the socket component. In the method, whenthe prosthetic hip joint is in the neutral position, a stem axisconnecting the center of rotation of the ball and a centroid of the stemat the mouth of the socket component is in a central zone between the atleast four extents. At least one of the steps of placing is performedwith the aid of a display of the position and/or orientation of the stemaxis relative to the central zone.

In the system described above, the inertial navigation devices can bereplaced with or supplemented by one or more cameras for monitoringdistance, linear position, or angular position.

In the system described above, the inertial navigation devices can bereplaced with or supplemented by one or more cameras for determining thespatial position of trackers coupled with instruments, such as a stylus.In such a system, the jig can be simplified without requiring moveableportions for example.

In some variations of the methods discussed herein, patient data can beused to enhance the accuracy of orientation of a component, such as theplane of the acetabulum. Patient data can include CT, MRI, X-Ray orother pre-operative planning data.

In another embodiment, a hip joint navigation jig is provided thatincludes a platform, a cannula coupling device, and a registration jigmounting feature. The cannula coupling device is disposed on theplatform and is configured to enable a cannula to be detachably coupledwith a bottom surface of the platform. The cannula is configured fordetachably coupling the platform with a bone adjacent to a hip joint.The registration jig mounting feature is disposed on the platform. Thehip navigation jig also includes registration jig. The registration jigincludes an upright member, a rotatable member, and a probe. The uprightmember is configured to be detachably coupled to the platform at theregistration jig mounting feature. The rotatable member is coupled withthe upright member for rotation about an axis that is not vertical whenthe jig is mounted to the bone adjacent to a hip joint and the uprightmember is disposed generally vertically. The probe had a tip forengaging anatomy. The anatomy engaging tip is disposed at a distal endof an elongate body coupled with the rotatable member for rotation aboutthe axis. The orientation and position of the elongate body of the probecan be adjusted to bring the anatomy engaging tip into contact with aplurality of anatomical landmarks during a landmark acquisitionmaneuver.

Although the platform can have any shape or configuration, it iselongate in some implementations, for example, including a first end anda second end. The first end can be configured to be oriented inferiorlyand the second end to be oriented superiorly when the navigation jig isapplied to the patient. If the platform is elongate, the cannulacoupling device can be disposed adjacent to the first end, which may belocated inferior of the second end when placed on the patient. Thecannula coupling device can be detachably coupled with a bottom surfaceof the platform in some embodiments. The registration jig mountingfeature is disposed on a top surface of the platform and can bepositioned adjacent to the first end. Again, the first end may beinferior end, just superior to or at the superior portion of thesurgical field.

In another embodiment, a hip joint navigation jig is provided thatincludes an anatomical interface comprising a bone engagement portion. Aregistration jig is also provided that is coupled, e.g., removeably,with the anatomical interface. A rotatable member is provided forrotation about an axis that is not vertical when the jig is mounted tothe bone adjacent to a hip joint and the registration jig is coupledwith the anatomical interface. An anatomy engaging probe is coupled withthe rotatable member for rotation about the axis and is translatable toenable the probe to be brought into contact with a plurality ofanatomical landmarks during a procedure. An inertial sensor is coupledwith the probe to indicate orientation related to the landmarks, thesensor being disposed in a different orientation relative to horizontalwhen the probe is in contact with the landmarks.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages are described belowwith reference to the drawings, which are intended to illustrate but notto limit the inventions. In the drawings, like reference charactersdenote corresponding features consistently throughout similarembodiments.

FIG. 1 is a perspective view of a hip navigation system applied to apatient illustrating a measurement of leg length and/or joint offsetafter implantation of the prosthetic hip joint.

FIG. 2 is an image of hip anatomy illustrating some examples ofanatomical landmarks that can be used in a method of navigating a hipprosthesis with the navigation system of FIG. 1.

FIG. 3 shows a navigation base assembly coupled with a first anatomicallandmark, in this case the ilium on the pelvis of the patient.

FIG. 4 is a perspective view illustrating first and second orientationdetecting devices coupled with the base of FIG. 3.

FIG. 5 is a perspective view of the navigating system, illustrating onetechnique for synchronizing a plurality of orientation and/or positiondetecting devices of the navigating system of FIG. 1.

FIG. 6 is a perspective view of the navigation system of FIG. 1 coupledwith the pelvis and illustrating a step of registering a landmark of afemur prior to resecting the femur.

FIG. 7 shows the anatomy after the femoral head has been resected and anoptional step of synchronizing a plurality of inertial sensors of thenavigation system.

FIG. 8 illustrates a step of registering an anatomical landmark disposedabout the acetabular rim on the pelvis.

FIG. 9 illustrates a step of registering another anatomical landmarkdisposed about the acetabular rim of the pelvis.

FIG. 10 illustrates initial placement of an impactor in the acetabulum.

FIG. 11 illustrates a hip prosthesis placement system, including aninertial sensing device.

FIGS. 11A-11C illustrate an embodiment of an impactor assembly.

FIG. 12 illustrates a step of navigating placement of a cup portion ofan artificial hip joint.

FIG. 13 is a perspective view of another embodiment of a hip navigationsystem.

FIG. 14 is a detail view of portion of the system of FIG. 13, with acamera recording linear position of a registration arm.

FIG. 15 shows a variation of the embodiment of FIGS. 13 and 14 in whichrotational orientation and linear position can be acquired by a cameraviewing a radial scale.

FIG. 16 is an exploded view of an assembly showing a tilt/rotationmechanism adapted to enable a camera to track at least one rotationalposition.

FIGS. 17-17C-2 illustrate modified systems configured for navigating aposterior approach hip replacement procedure.

FIGS. 18-21B illustrate a hip navigation system configured for ananterior approach hip replacement procedures, and various aspects ofsuch procedures.

FIGS. 22-31 illustrate various aspects of methods involving custompatient-specific positioning jigs.

FIG. 32 illustrates methods for defining a patient-specific safe zone ina hip placement procedure.

FIG. 33 is an embodiment of a system for close range optical tracking.

FIGS. 34-35 illustrate various anatomical landmarks that can be used invarious methods involving navigating with landmarks.

FIG. 36 is a pre-operative image that can be used to enhance alignmentin a hip procedure by providing patient specific data.

FIGS. 37 and 38 are views of a hip procedure navigation system appliedto a pelvis in a posterior approach.

FIGS. 39 and 40 are view of the hip procedure navigation system of FIG.37-38 modified and applied to a pelvis in an anterior approach.

FIGS. 41-41A illustrate a first embodiment of pin securement devices.

FIGS. 42-42B illustrate a second embodiment of pin securement devices.

FIGS. 43-43B illustrate a third embodiment of pin securement devices.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A variety of systems and methods are discussed below that can be used toimprove outcomes for patients by increasing the likelihood of properplacement of a hip joint. These systems can be focused on inertialnavigation techniques, close range optical navigation, or a combinationof inertial and optical navigation.

I. Hip Navigation Using Inertial Sensors

Systems and methods described below can improve prosthetic hip jointplacement using navigation in connection with referencing anatomicallandmarks, incorporating preoperative custom fit jigs based on imaging,and a combination of pre-operative imaging and landmark referencing.These hip procedures generally guide a prosthetic hip to an orientationwithin the acetabulum that minimizes the chance of dislocation due toimpingement of the femoral neck on the cup or on bones around theacetabulum or other reasons related to suboptimal orientation of theprosthetic. Various techniques leverage population averages of properplacement while others are amenable to patient specific refinements.Also various techniques for registering and confirming the positionand/or orientation of the femur pre- and post-implantation are discussedherein, which are useful to control leg length and joint offset at theend of the procedure.

A. Navigation Using Inertial Sensors and Jigs for Referencing AnatomicalLandmarks With Posterior Approach

Most hip replacement procedures presently are performed from a posteriorapproach. In this approach, the patient is positioned on his/her sideand the anterior pelvic plane is oriented vertically, e.g.,perpendicular to the plane of the table on which the patient ispositioned. Most surgeons performing hip replacement are very familiarwith this approach and will immediately recognize the benefit ofenhanced certainty about the orientation of the relevant anatomy whenthe patient is in this position.

1. Apparatuses and Methods for Posterior Approach Hip Navigation

FIGS. 1 and 4 show a hip navigation system 100 adapted to navigate a hipjoint procedure with reference to anatomical landmarks withoutrequiring, but not necessarily excluding, pre-operative imaging or otherinputs apart from those discussed below. The system 100 is shown mountedon a pelvis in a posterior approach in FIG. 1. FIG. 4 shows an earlyphase of a procedure prior to the joint being dislocated but after thesystem 10 is mounted to the pelvis. FIG. 1 shows a late phase of somevariations of techniques for which the system 100 is adapted. Asdiscussed further below, such variations involve registering the femurprior to and after the joint is replaced to confirm an aspect of therelative position and/or orientation of the femur, e.g., leg length,joint offset, and rotational orientation of the femoral neck.

The system 100 includes a registration jig 104, an alignment assembly108 and a landmark acquisition assembly 112. The alignment assembly 108is rigidly connected to the hip in the illustrated configuration so thatmotion of the hip cause corresponding motion of sensor(s) in theassembly 108 as discussed below. Sensing this motion enables the system100 to eliminate movement of the patient as a source of error in thenavigation. The landmark acquisition assembly 112 provides a full rangeof controlled motion and sensor(s) that are able to track the motion, inconcert with sensor(s) in the assembly 108. Additional details ofsystems, devices, sensors, and methods are set forth in U.S. Pat. No.8,118,815; US2010/0076505; and U.S. Pat. No. 8,057,479 which are allincorporated by reference herein in their entireties for all purposes.The sensors in assemblies 108, 112 preferably transfer data amongthemselves and in some cases with external devices and monitorswirelessly, using Bluetooth, Wifi® or other standard wireless telemetryprotocol.

The registration jig 104 includes a fixation cannula 124 that has adistal end that can be advanced to a pelvic bone at an anatomicallocation or landmark or other selected location. In the illustratedtechnique, the cannula 124 is secured by a pin 132 (see FIG. 3) that isdriven into the ilium on the pelvis through the cannula 124. A distalend 128 of the pin 132 is shown in FIG. 1.

As discussed further below, the cannula 124 can be coupled with otherbones in other techniques with a posterior approach. For example, thecannula 124 can be coupled with the ischium or the pubis in othertechniques. In some techniques, the cannula 124 is mounted to a pelvicbone but not at a landmark. The hip navigation system 450 discussedbelow in connection with FIG. 17-17B can be used such that the fixationmember 466 is coupled at a point superior to the superior-most point onthe acetabular rim. In a specific technique, the member 466 is about 10mm above the superior-most point on the acetabular rim. In suchtechniques, three or more anatomical landmarks disposed about theacetabulum can be acquired, as discussed below. When the cannula 124 iscoupled with a landmark, only two additional landmarks are acquired insome embodiments as discussed below. In another variation, a clamp canbe used to couple with a bone without requiring that the pin 132 bedriven through the cannula 124 into the bone. For example, if the boneis thinner in the region where the system 100 is to be anchored, placingthe pin may be disadvantageous. FIG. 2 shows a region where a clamp maybe used beneath the point “A” on the ischium. One reason for mounting orclamping the cannula 124 away from the landmarks is that the landmarksmay not be visible or accessible before dislocating the hip joint. Ifthe clinician wishes to use the system 100 to reference the femur (asdiscussed below), it may be required to mount or clamp the cannula 124away from the landmarks.

FIG. 1 illustrates a step toward the end of a navigated hip jointimplant procedure discussed in detail below. Some of the preceding stepsinvolve removing the to-be-replaced joint, navigating the hip joint,preparing the implant location for the artificial joint, and placing thejoint, as elaborated below. As discussed further below, FIG. 1illustrates a technique for confirming that these steps were properlyperformed.

FIG. 2 shows some of the anatomy that is relevant to various methods andsystems herein. In some embodiments, the navigation system 100 isconfigured to locate a relevant anatomical feature to aid in properplacement of a prosthetic hip joint. For example, a plane can be locatedusing the system 100 that includes at least a portion of a patient'sacetabular rim. In practice, the acetabular rim may be uneven due todevelopment of ostephytes. So, in the context of this applicationlocating the anatomical plane can be an approximation of the actualtopography, for example an estimate of the plane, a plane including asubstantial fraction, e.g., a majority of the surface of the acetabularrim, or some other manner of estimating a relevant anatomical feature.Preferably the anatomical landmark being located is used to confirmaccurate placement of at least the cup and preferably the completeartificial hip joint.

FIG. 2 also shows an example of anatomical landmarks that can be used toapproximate the acetabular rim or another plane relevant anatomicallandmark. In many patients the acetabular rim is not well defined, dueto injury, advanced stages of arthritis or other conditions.Accordingly, approximating the acetabular rim for these patientsincludes calculating in the system 100 a plane that references but maynot include most or any of the actual acetabular rim. The plane that isdefined is located near the rim but more importantly has a knownanteversion and abduction angle relative to the anterior pelvic plane.For example, three points can be used to estimate the plane of theacetabular rim. In one technique, some or all of the points illustratedin FIG. 2 are used.

As illustrated by FIG. 2, three landmarks are defined at “A”, “B”, and“H”. The landmark “H” is located on the ilium at a location that isspaced away from the rim by an amount sufficient to avoid irregular bonygrowth due to injury, advanced stages of arthritis or other conditions,for example 1 cm superior to the most superior point on the acetabularrim. The landmarks “A” and “B” can be located on the ischium and pubisrespectively and can be similarly spaced from the rim to avoiddamaged/diseased areas. Each of these landmarks preferably is closeenough to the rim, however, to be within the standard open area, e.g.,the area exposed by the surgical cut down. Other landmarks that could beused include: anterior insertion point of trans-acetabular ligament tothe ischium, mid-point of the inferior aspect of the acetabular notch,the anterior superior iliac spine, anterior inferior iliac spine,convergence of the acetabulum and anterior inferior iliac spine, as wellas the other landmarks illustrate on FIGS. 34 and 35. In the techniquesdiscussed below all of the ilium, the pubis, and the ischium are used tolocate the acetabular rim. The navigation system 100 has one or moreprocessors that receive(s) data and determines the relative position ofthese (or other) anatomical landmarks from these points. The data can begenerated by inertial sensors, as discussed elsewhere herein, or othertypes of sensors. Preferably the sensors are small enough to be mountedon or in handheld housings or embedded in the instruments. Thenavigation system 100 preferably also has a memory device to at leasttemporarily store the position of these points or relevant orientationdata.

FIG. 3 shows further details of the registration jig 104 and furtheraspects of methods of navigating an artificial hip joint. A proximal endof the pin 132 is coupled with or disposed above a platform 136 that isconfigured to couple with the alignment assembly 108 and/or the landmarkacquisition assembly 112. As shown in FIG. 1, the platform 136 can beconnected to both of the alignment assembly 108 and the landmarkacquisition assembly 112 at the same time. The platform 136 comprises arigid bar fixed to the proximal end of the pin 132 and/or the cannula124 in the illustrated embodiment. The platform 136 includes a pluralityof mount features 140A, 140B, e.g., a mount feature on each of twolateral ends 144A, 144B of the platform. The mount feature 140A isconfigured to permit non-rotational attachment to the alignment assembly108.

FIG. 3 illustrates that the registration jig 104 is configured to beused in left and right hip procedures, for example having a dedicatedmount feature 140A for each hip. Preferably the mount feature 140Aprovides a post spaced away from the joint being treated so that thealignment assembly 108 can be mounted as far away from the hip joint aspossible. FIG. 5 shows the alignment assembly 108 on this post andanother post exposed. The exposed post is not used during the procedureon the hip joint illustrated in FIG. 5. However, if the other hip of thepatient is being treated, the platform 136 is in the oppositeorientation and the posted exposed in FIG. 5 will be coupled with thealignment assembly 108. Stated another way, a longitudinal axis of theplatform 136 extends between two mount posts, each of which can bededicated to a hip on one side of the medial-lateral mid-plane of thepatient.

The mount feature 140B enables rotational mounting of the landmarkacquisition assembly 112. For example, the mount feature 140B caninclude a pivotally mounted jig 148 that projects upward to a free endthat is adapted to mate with an orientation sensing device as discussedbelow. The joint 148 permits a registration arm, such as the elongatemember 224 discussed below to be tilted downward to touch landmarks atdifferent elevations.

In one technique, the registration jig 104 is preassembled and is driveninto a suitable anatomical landmark, such as the ilium. In othertechniques, an anchor jig can be mounted off-set from a landmark to beacquired. The ilium will have been previously identified by conventionalmeans, such as by X-ray examination, palpation, or by making an incisionand visually inspecting the pelvis. In one technique, the cannula 124,the pin 132, and the platform 136 are separable so that the pin can beplaced and the platform 136 coupled to the pin at a later time. Thecannula 124 can be coupled with other landmarks in some variations.

FIG. 4 illustrates further steps of various techniques. For example, thealignment assembly 108 can be coupled with the mount feature 140A. Inone embodiment, the alignment assembly 108 includes a rigid extension160 that is adapted to be mounted detachably to the mount feature 140A.The extension 160 has a first end 164 and a second end 168. The secondend 168 is detachably mountable to a surgical orientation device 172that detects orientation and rotation of the device 172 relative to areference frame. The orientation device 172 preferably comprises atleast one sourceless sensor, such as an accelerometer, a gyroscope, or acombination of these sensors and other sensors. In one preferredembodiment, the orientation device includes a three axis accelerometerto detect orientation relative to gravity and a plurality of gyroscopesto detect rotation. Other sensors could be used in variousmodifications. Examples of specific sensor combinations include AnalogDevices ADIS 16445 and Invensense MPU-6050 or MPU-9150 among others. Insome approaches, the orientation device 172 can be disposable and so thesensors preferably are less expensive sensors. Sensors on the landmarkacquisition assembly 112 may be reusable in some configurations and thusmay incorporate more expensive, more rugged or more accurate sensors.

The first end 164 of the detachable extension provides severalfunctions. The first end 164 has a device to engage the mount 140A in asecure but releasable manner. The engagement between the extension 160and the platform 136 minimizes or prevents relative movementtherebetween to avoid any mechanical relative movement during navigationprocedures so that movement of the orientation device 172 corresponds tomovement of the hip. The first end 164 also has a docking device that,as discussed further below, provides a stable and controlled manner toposition the landmark acquisition assembly 112 relative to theorientation device 172.

FIG. 4 also illustrates that the landmark acquisition assembly 112 canbe securely coupled to the platform 136, e.g., at the mount 140B. In oneembodiment, the landmark acquisition assembly 112 includes a gimbaledjig 200 and an orientation sensing device 204. The jig 200 includes acoupler 208 for detachably coupling with the mount feature 140B of theplatform 136. The coupler 208 is pivotally connected to a slidingsupport 212. The sliding support 212 includes a slot that permitsslideable extension of an elongate member 224. The slideable extensionpermits a range of motion of a distal end 228 of the elongate member tofacilitate acquiring a plurality of landmarks that are differentdistances from the attachment location of the cannula 124, as discussedfurther below. In other words, the distal end 228 can be extended awayfrom the axis of the sliding support 212 or can be retracted to aposition closer to the axis of the sliding support 212.

FIGS. 4 and 6 illustrate the moveability of the landmark acquisitionassembly 112 relative to the platform 136 between two positions. In FIG.4, the elongate member 224 is swung about an axis that may be parallelto a longitudinal axis of the cannula 124 to move the distal end 228away from the first end 164 of the extension 160. This is a movingconfiguration of the gimbaled jig 200. In addition to rotation enabledby the pivotal coupling between the coupler 208 and sliding support 212,the pivotally mounted joint 148 can enable the elongate member 224 topivot about an axis that is not parallel to the axis of the cannula 124.The axis of rotation of the joint 148 can be perpendicular to the axisof rotation of the sliding support 212. This rotatability enables thedistal end 228 of the elongate member 224 to pivot down to contactanatomical landmarks, as discussed above. Additionally, the slideabilityof the elongate member 224 within the sliding support 212, discussedabove, enables the distal end 228 to move to reach anatomical landmarksin the same plane but closer to or farther from the distal end of thecannula 124 or pin 132. FIG. 6 shows the distal end 228 of the elongatemember 224 positioned closer to the platform 136 for referencinglandmarks at higher elevation or closer positions, e.g. on the lateralside of the femur.

FIG. 4 also shows that the distal end 228 can include an angled lengththat enables the elongate member 224 to avoid minor irregularities inheight adjacent to the anatomical landmarks being registered. Suchirregularities may be normal anatomy, osteophytes or irregular bonegrowth of various types.

FIG. 5 illustrates a parked configuration 260 of the landmarkacquisition assembly 112. In particular, a portion of the elongatemember 224 is moved into a latch 262 disposed at the first end 164 ofthe upright extension 160. The parked configuration 260 enables thenavigation system 100 to manage errors that can compound in someinertial sensors. For example, in one embodiment, gyroscopic sensors inthe orientation device 172 and in the orientation sensing device 204 canbe synchronized when a stable and known orientation is detected and oneor more of the gyroscopes, e.g., the gyroscope in the device 204, can bezeroed after that condition is met. Further techniques employing theparked configuration 260 will be discussed further below. As discussedbelow in connection with the system 450, some jigs have a registrationpoint adjacent to the distal end of the anchor jig or bone connectionsite. The system 450 is capable of accurately acquiring landmarks basedon only accelerometers operating in the device 204 in one mode. In sucha mode, a registration feature can provide an analogous function to theparked configuration, e.g., to enhance accuracy of the sensing devicesin the system.

Another example of a parked configuration of the system 100 can beprovided. For example, the parked configuration advantageously includesthe ability to stably position and hold the devices 172, 204 forsubstantially no relative movement. In one approach, the orientationsensing device 204 is mounted on the rigid extension 160. Otherarrangements could include a mounting post on the platform 136 adjacentto the rigid extension 160.

Where error management is less an issue, the parked configuration 260can still be useful in that it prevents unwanted swinging or othermovement in the surgical field.

In one basic method, the jigs discussed above are connected to thepelvic bone, the system 100 is put into the parked configuration 260,and the sensors are initialized. The initializing can includesynchronizing at least two sensors. In some cases, the initializing caninclude zeroing one or more sensors. In this context, “zeroing” is abroad term that includes any method of eliminating accumulated error inthe system, including any form of resetting of the sensors, and/orconfirming in one device that the data from the other device is reliablefor at least a fixed period.

FIG. 6 illustrates an optional step of acquiring a landmark of a femurin connection with a hip replacement procedure. The hip is positioned ina neutral flexion/abduction position. The landmark acquisition assembly112 is in a withdrawn configuration 266 with the elongate member 224moved, such as by sliding in the sliding support 212, to accommodate therelatively short distance from the platform 136 and a landmark of theproximal femur. In one technique the tip of the distal end 228 isbrought into contact with a part of the greater trochanter or elsewhereon the proximal femur. After the landmark is found and/or contacted, theclinician can make a mark on the femur Fm, such as a bovie mark, a penmark, a stitch or other durable indication. Once the tip of the distalend 228 is in contact with the desired landmark, the navigation system100 processes data from and stores the orientation of one or moresensor(s) in the orientation sensing device 204. Additionally, in someembodiments, the elongate member 224 is provided with a scale 226indicating position of the tip of the elongate member 224, e.g.,relative to the cannula 124 or some other relevant fixed feature of thepatient or the system 100. By providing the scale 226 to be read by theclinician, the system is made simple and cost effective.

After the optional step illustrated in FIG. 6, the proximal femur can beresected to remove the natural ball thereon.

FIG. 7 illustrates that in one advantageous technique, the user returnsthe system 100 to the parked configuration 260. This step may beoptional depending on the sensor(s) and the timing of the resecting ofthe femur. In this position, the sensor(s) in the orientation devices172, 204 can be initialized again, e.g., zeroed. As discussed above,this is one technique for minimizing accumulation of error in someinertial sensors. By providing this optional step, less costly sensorscan be used enabling the system 100 to deliver highly accurate hipreplacement while helping to manage cost for the patient, medicalprovider and healthcare system generally.

FIG. 8 illustrates a first extended configuration 264 provided in a stepafter the resecting of the proximal femur in which a second anatomicallandmark is acquired or referenced. In particular, the elongate member224 can be extended and can be rotated by the jigs 148, 200 to be incontact with any suitable landmark. In one technique, contact is madebetween the distal end 228 and the ischium. To provide maximum accuracy,this contact may be provided within a short period, e.g., within about20 seconds of being disengaged from the parked configuration 260. Oncecontact is made, the system 100 is configured to store the orientationof the sensing device 204. In one configuration, the orientation isstored after a button or other indirect means is pressed on theorientation device 172. In addition to acquiring the orientation, aposition value is input to the system. For example, the scale 226 on theelongate member 224 can be read by the user and the value of the scaleinput into the system. In one technique where the scale 226 is read andinput by the user, the orientation device 172 has a user interface withan input device for inputting such variables. As can be seen in thedrawings, the scale 226 can in fact be two different scales, one foreach of the retracted configuration 266 and the extended configuration264. Alternatively, the scale 226 can extend the entire length of theelongate member 224 to provide a greater range of positions that can beread by the clinician or by the system as in FIGS. 13 and 14.

The extended configuration 264 is one in which the distal end 228 of theelongate member 224 is adapted to touch an anatomical landmark locatedbetween the medial cephalad-caudal plane of the patient and theacetabulum of the pelvis.

Depending on the sensors used and the timing of landmark acquiring stepof FIG. 8, the user may return the system 100 to the parkedconfiguration 260 and also may initialize, e.g., zero, the system 100again.

FIG. 9 illustrates a second extended configuration 272 provided in astep after the resecting of the proximal femur in which a thirdanatomical landmark is acquired or referenced. The third anatomicallandmark can be acquired before the second anatomical landmark in sometechniques. In the second extended configuration the distal end 228 ofthe elongate member 224 moved to contact a landmark, such as the pubis.To provide maximum accuracy, this contact may be provided within a shortperiod, e.g., within about 20 seconds of being disengaged from theparked configuration 260. Once contact is made, the system 100 can storethe orientation of the sensing device 204. The orientation can be storedby pushing a button or other user interface device. In some techniquesorientation and position are input into the system. For example, thescale 226 on the elongate member 224 can be read by the user and thevalue of the scale input into the system. In one technique where thescale is read and input by the user, the orientation device 172 has aninput device, such as a user interface for inputting such variables.

The extended configuration 272 is one in which the distal end 228 of theelongate member 224 is adapted to touch an anatomical landmark locatedanteriorly of the acetabulum.

Once landmarks have been acquired, the system 100 can determine thebearing of three landmarks including that of the attachment location ofthe cannula 124, if the pin is attached to a relevant landmark. Thesystem can calculate the orientation of the orientation device 172relative the plane containing these three (or in other methods anothergroup of three or more) landmarks. From this, a variety of postprocessing can be performed. For example, the orientation (anteversionand/or abduction) can be adjusted based on the known mean orientation ofthe plane containing these three (or another three or more, if used)landmarks from the pelvic anatomic reference planes.

One variant of the system 100 enables a user to select between multiplesets of landmarks for use in the above calculations. The methoddiscussed above exploits the use of three points that are off of theacetabular rim. These points are less impacted by local prominences atthe rim that may be due to disease or deformity. Thus, they have a lowerlikelihood of requiring intra-operative improvisation. On the otherhand, another set of landmarks can be selected where the rim is free ofdeformities, which might be confirmed pre-operatively. For example, twoor three points can be selected on the acetabular rim for landmarkacquisition. The on-rim landmarks are advantageous in that they areeasier to access through a smaller incision. For example, on-rim pointscan include the center of the posterior insertion of the transacetabularligament, the center of the anterior insertion of the transacetabularligament and the most superior point on the rim. A group of anatomicallandmarks including one or more extra-acetabular landmarks can includethe ilium (where the registration jig 104 or other anchor member can beinserted), the lowest point of the acetabular sulcus of the ischium, andthe prominence of the superior pelvis ramus.

Some techniques involve referencing a fourth point. The fourth point canbe used in connection with some forms of patient specific registration.The fourth point can be extra-acetabular or can be disposed on theacetabular rim. An example of an acetabular landmark is the acetabularnotch. Other landmarks are discussed herein, for example in connectionwith FIGS. 34 and 35.

The posterior approach systems are advantageously configured to allowintra-operative selection between on-rim and off-rim points. Forexample, if the rim looks free of deformities pre-operatively but whenexposed presents differently, the surgeon can select an off-rim landmarkset.

Several techniques for enhancing the accuracy of the relationshipbetween the sensed landmarks and the location of calculated anatomicalfeatures, such as the anterior pelvic plane or angle of the acetabulumcan be employed. For example, user input can be collected indicatingwhether the hip being treated is on the left or the right side of thepatient and whether the patient is male or female. A more refinedestimation of the model can be provided based on a characterization of astudy group. For example, hip joints of a group of 30 or more patientscan be studied to identify the correspondence between a feature that canbe accessed in one approach and an anatomical feature of more surgicalrelevance that cannot. A group of subjects can be studied for any numberof demographic characteristics such as gender, age, weight, height orany other variable in a relevant population. For those sub-groups, acorrelation or transformation between a measured parameter and aparameter that cannot be measured but is desirable to know can begenerated. Once such a correlation or transformation is established,transforming a measured feature into the unmeasurable but useful to havefeature can be achieved by operating software on a processor. Thesoftware can be programmed to calculate one or two angles, e.g.,inclination and anteversion based on a registered pelvic plane, such asa proxy acetabular plane. Such a system can be used to generate in realtime the angles of a free hand instrument relative to the anatomy, e.g.,relative to an acetabulum in placing a hip socket component.

Additionally, data from the use of pre-operative imaging or positioning(discussed below) can be used to enhance the accuracy of thesecalculations. Thus, the posterior approach systems preferably areconfigured to take user input directly by actuating buttons on theorientation device 172 or by connecting an auxiliary data storagedevice, such as a flash memory device, to the system or by any means ofother communication with the system, including wifi connection,Bluetooth, Internet connection among others.

In some techniques, the posterior approach systems described herein areadapted to determine, monitor, and confirm proper leg length and jointoffset outcome in a hip replacement. For example, the system 100 cancalculate and store components of a leg length metric, e.g., a vectoralong the superior-inferior axis (leg length) and/or along themedial-lateral axis (offset). In one approach, the device 172 has adisplay that indicates when the femur is in the same position pre- andpost-operatively. For example, it can indicate “0” meaning nodisplacement causing a leg length change and “0” indicating no movementof the femur farther away from the cephalad-caudal mid-plane of thepatient pre- and post-operatively. For enhanced accuracy, a plurality ofpoints, e.g., three points, can be marked acquired and/or marked on thefemur. The points can be spaced apart by an amount sufficient to provideincreased accuracy. These three points can be used to confirm properplacement of the femur in abduction, rotation, and flexion.

One enhancement involves referencing the femoral neck to assure thatafter implanting the hip joint, the femur is positioned properlyrotationally. For example, it may be desired to make sure that a featureof the femur like the greater trochanter resides in the same rotationalorientation relative to an axis extending through the center of rotationof the femoral head and perpendicular to the plane of the acetabulum. Toassure a substantially unchanged rotation orientation post-implantation,the system 100 can record one or more, e.g., three points on the femoralneck pre- and post-implantation. Three points that would be convenientfrom either the posterior approach or the anterior approach (discussedbelow in connection with FIGS. 18-21) are the greater trochanter, lessertrochanter and the insertion of the obdurator externus.

The foregoing are some steps that can be used to determine and store avariety of parameters useful in a navigated hip procedures. After someor all of these steps have been performed, in one embodiment, theacetabulum can be prepared for receiving a cup. For example, theacetabulum can be reamed in a conventional manner. In some embodiments,the reamer can be coupled with an orientation device containing aninertial sensor to guide the reaming process. This is discussed in somedetail in US2010/0076505, published Mar. 25, 2010 which is incorporatedby reference herein in its entirety for this purpose and for alldisclosure therein generally.

FIG. 10 shows that after reaming, an impactor 300 may be used to place acup of an artificial hip joint. The impactor handle 304 may bepositioned in the approximate correct orientation, e.g., with alongitudinal axis of the impactor being disposed perpendicular to theplane navigated above or a plane determined based on the navigatedplane. FIG. 10 shows that this initial placement can be done while thesystem 100 is in the park configuration 260. The impactor 300 can besubstantially aligned at this time, based on visual inspection. As partof the step illustrated in FIG. 10 or shortly thereafter, the sensorscan be initialized, e.g., zeroed as discussed above.

FIG. 11 shows that in a subsequent step the orientation sensing device204 can be undocked from the proximal end 230 of the elongate member 224and thereafter docked to the impactor 300. Preferably this step isperformed while the impactor 300 is in place on the hip, close theproper alignment. In another embodiment, a third sensing device similarto the sensing device 204 be coupled with, e.g., pre-attached to, theimpactor and the data collected above transferred to the third device.The impactor 300 and sensing device 204 comprise a cup orientationnavigation assembly. Preferably the impactor 300 has a cylindrical shell312 that is moveable relative to an inner shaft 316 of the handle 304.The shell has a docking device 320 that can receive the docking deviceof the sending device 204. The moveability of the shell 312 helps toisolate the sensing device 204 from the forces that are transmittedthrough the impactor 300. These forces are applied by a mallet or otherdevice for forcibly moving the cup into position. By providing at leastsome force isolation between the shell 312 and the sensing device,impact on the sensors in the sensing device 204 can be reduced.Excessive force being applied to the sensing device 204 can put thedevice 204 out of service, for example until synched with the device172.

FIG. 11A illustrates a further embodiment of an impactor 300A in whichthe movement of a shell 312A is cushioned by a plurality of springmembers 340, 344 which are configured to absorb at lease some of theshock of the impact on the impactor 300A. The impactor 300A also isconfigured to be modified to suit any of a plurality of hip prostheses.For example, a plurality of tip components 348 can be provided in a kitwhere each tip component is attachable to and detachable from a distalend of the shaft 316A of the impactor 300A.

FIGS. 11B-C show more detail of distal features of the impactor 300A. Inparticular, the tip component 348 is removable from a shaft 316A of theimpactor 300A. FIG. 11C shows that the tip component 348 can have arecess 352 formed on the proximal side thereof and an engagement device356 formed on the distal side thereof. The recess 352 can comprises aplurality of flats 350A corresponding to a plurality of flats 350B onthe distal end of the shaft 316A. The flats permit proximal-distalsliding of the recess 352 over the distal end of the shaft 316A.Preferably a detent device or other mechanism is provided between thetip component 348 and the shaft 316A so that the component does not falloff the shaft. The flats prevent the tip components 348 from rotatingrelative to the shaft 316A. The engagement device 356 comprises threadsin one embodiment so that the cup 360 of the prosthetic hip can bescrewed onto the distal end of the tip component 348. The slidingengagement of the tip component 348 on the shaft 316A is importantbecause the impactor 300A is intended to be used with hip prostheses ofa variety of manufacturers. Often the cup 360 will have a hole patternfor securing the cup to the prepared acetabulum that is unique to themanufacturer and that is dictated by the anatomy. The flats enable manydiscrete alternate relative angular positions of the tip component 348(and hence the cup 360) to the shaft 316A. A plurality of flutes orelongate axial ridges 364 on the outer surface of the tip component 348enable the user to securely grasp the tip component for mounting anddismounting the tip component on the shaft 316A.

FIG. 12 shows the cup orientation placement navigation assembly of FIGS.11A-C adjacent to the anatomy. This figure also illustrates a free-handnavigation configuration 274, in which at least the orientation devices172, 204 are capable of six degrees of motion relative to each other.Any of the variations of FIG. 11A-11C could be substituted in theillustration. In particular, the handle 304 is oriented as desired. Inone embodiment, the system 100 displays in real time the angle of thecup relative to the navigated plane, which was acquired as discussedabove. Angles that can be displayed include any one or more ofanteversion and abduction for example. Preferably the clinician canconfirm the position of the cup within a short fixed time, such aswithin about 20 seconds. In one embodiment, the angles displayed can beadjusted by about 40 degrees abduction and 20 degrees anteversion. Theseangles are not critical, but they relate to the range of motion of theleg. It is preferred to be close to these angles because motion inabduction and anteversion extends on either side of these angles. It isbelieved that the systems discussed herein can increase the percentageof patients in a “safe zone” close to these angles, typically describedas within 10 degrees of these angles. In contrast, studies show thatconventional techniques yield close to 50% of patients outside the “safezone.”

Depending on the sensors and the timing of cup placement step of FIG.12, the user may mount the sensing device 204 on the elongate member 224again and may return the system 100 to the parked configuration 260 andalso may initialize or zero the system 100.

The system 100 can be configured to provide a pre- and/or post-operativeestimation of an angle relative to the angle of the table. In theposterior approach, the patient is placed on his/her side. In thisapproach, there is more chance for the patient's position to shiftintra-operatively. In one embodiment, an alignment rod can be coupledwith the sensing device 204 and aligned with the plane of the table. Theorientation of the sensing device 204 when so aligned is recorded in thesystem. Later in the procedure, one or more angles is calculated anddisplayed to the user based on the assumption that the pelvis has notmoved. At such later stages, the orientation of the sensing device 204can be confirmed again relative to the table to provide informationabout whether the patient has moved. If significant movement hasoccurred, such that any assumptions of no movement are violated, some orall of the landmark acquisition steps can be repeated. Alternatively,the movement of the pelvis can be tracked by the sensing device andcorrected for. The manner of incorporating the table orientation withlandmark acquisition is discussed in greater detail below.

The user will have placed the artificial ball of the replacement hipjoin in the proximal femur and thereafter can place the ball in the cup,which was properly oriented using the techniques discussed above.

FIG. 1 shows that thereafter, the user can optionally confirmorientation and/or leg length using the system 100. The leg with theartificial hip joint assembled is placed in a neutral flexion and/orabduction and/or rotation position. The acquisition assembly 112 can beplaced in the retracted configuration 266. The distal end 228 of theelongate member 224 can be brought into contact with a landmark, whichmay be the same landmark acquired in FIG. 6. Once contact is made withthis landmark (e.g., the bovie mark), the orientation of the sensingdevice 204 is determined by the system 100. Also, the distance indicatedon the scale 226 of the elongate member 224 is input into the system inany of the manners discussed above (e.g., manual or sensed). The system100 can thereafter calculate components of vectors along the S-I axis(leg length) or M-L axis (offset).

Once leg length and offset are determined post-operatively, they can becompared the pre-operative measurements (FIG. 6) to let the surgeon knowif any adjustments should be made before completing the hip replacementsurgery.

FIGS. 13 and 14 show other embodiments of a hip navigation system 400that can include any of the features discussed above. In addition, thesystem 400 includes a free-hand sensor mount 404 that can be used tomount a freehand orientation device 204A in one configuration. Thefreehand orientation device 204A preferably includes inertial sensors,similar to those hereinbefore described. The device 204A preferably alsoincludes a camera 412. The field of view is illustrated by the coneprojecting downwardly from the base of the freehand orientation device204A. FIG. 14 shows that the field of view includes a window 418 in asliding support 420. The window 418 enables the scale 226 to be viewedtherethrough.

Because hip replacement procedures involve an open surgical field with asubstantial amount of exposed tissue and blood the line of sight thecamera 412 to the scales can become obstructed. In one embodiment, ahood is provided above the window 418. The hood keeps most of the bloodand tissue out of the space where the camera views the scales.Additionally, a scrubber component, e.g., a thin rubber member, can beprovided above the scales 226, 226A (discussed below) to prevent thistissue or fluids from entering into the field of view laterally.

One advantage of the system 400 is that the camera 412 can automaticallyprocess the image captured through the window 418 and thereby determinethe position of the elongate member 224 relative to the sliding support420. A further advantage of this is to eliminate one step from thenavigation process, e.g., to eliminate the need to enter the lineardimension into the system 400. Eliminating the step can reduce timeand/or personnel in the operating room. Also, the camera 412 can beconfigured to read a much higher resolution than can be read by aclinician. This can provide greater accuracy in the system overall. Notonly that, but the camera can be configured to make fewer or no errorsin reading the position, which can improve outcomes overall. Forexample, miniature cameras can produce data in JPEG or other imageformat that a processor in one or both the orientation devices 172, 204Acan process to extract the linear position of the elongate member 224.

A further modified embodiment is described in FIG. 15, which shows anarcuate scale 226A that can be positioned on a structure beneath theelongate member 224, e.g., on a structure beneath the orientation device204A that is rotationally fixed relative to an axis extending out of thepage. FIG. 16 shows one configuration with this arrangement. A pivot 440enables the sliding support 420 to rotate about an axis extending upwardon the page. Although the pivot 440 is fixed about this upward extendingaxis, it can rotate about a pivot 444. A window 418A in the elongatemember 224 enables the camera to see through the support to view thescale 226A disposed on an arcuate or disk shaped feature of the pivot440. The scale 226A can be read by the camera 412 or a second camera toprovide accurate determination of the rotational position of theelongate member 224. This can enable one of the sensors in theorientation device 204A to be eliminated or inactivated. In anotherembodiment, camera date derived from the scale 226A can be used toconfirm the data from sensors in the orientation device 204A. Preferablythe scale 226A has markings over a range of from about 15 to about 90degrees, for example, between about 30 and about 60 degrees, e.g., atleast between about 40 and about 50 degrees.

2. Posterior Approach Systems Adapted for Accelerometer Sensitivity

FIGS. 17-17B illustrate another embodiment of a system 450 fornavigating a hip procedure from a posterior approach. The system 450includes an anchor jig 454, an alignment system 458, and a landmarkacquisition assembly 462. The components may be similar in some respectsto those discussed above, and such descriptions are incorporated withthis embodiment where consistent.

The jig 454 includes a hollow fixation member 466 and a platform 468 forcoupling a plurality of devices to the pelvis. The platform has agenerally T-shaped configuration including a first portion 468A coupledwith the proximal end of the fixation member 466 and a second portion468B disposed transversely to the first portion 468A. The first portion468A provides a support for a cradle 476 discussed further below. Thesecond portion 468B can include a plurality of docking devices 469 forcoupling directly or indirectly with the orientation device 172. TheT-shaped configuration provides the advantage that the docking devices469 can be disposed father away from the surgical site than is the casewith the system 100. This reduces any intrusion of the orientationdevice 172 into the working field.

In some cases, the fixation member 466 provides adequate stability inanchoring the system 450 to the pelvis. In other situations, the jig 454can be coupled with the pelvis from the second portion 468B. Forexample, a slot 470 can be formed in the second portion 468B on one orboth sides of location where the first portion 468A extends from thesecond portion 468B. The slots 470 can extend from a lateral edge of thesecond portion 468B toward location where the first portion 468A extendsfrom the second portion 468B. The slots 470 can include a plurality ofchannels 471 configured to receive fixation pins (e.g., Steinmann pins)that can be advanced into the pelvis. The channels 471 extend generallyparallel to the fixation member 466. The fixation pins can be securelyconnected to the second portion 468B in the channels 471 by a clampdevice 472. The clamp device can include a screw configured to draw theportions of the second portion 468B on either sides of the slot 470toward each other and thus to create large frictional forces on the pinsin the slots 471.

The slots 470 preferably are aligned such that a plane extends alongboth of the slots 470 along their length. Because the slots 470 are longand slender this plane can be readily visualized in an X-ray image. Itis preferred that the jig 454 be aligned to the pelvis such that theplane extending along the slots 470 is perpendicular to an axis of thepatient (e.g., the intersection of the medial lateral plane and thetransverse mid-plane of the patient). This feature provides a convenientway to visually confirm proper positioning of the jig 454 in oneembodiment.

The fixation member 466 includes a registration feature 473 and a foot474 adjacent to a distal end thereof and a coupling 475 adjacent to theproximal end thereof for connecting to the platform 468. The foot 474includes a plurality of spaced apart spikes extending from a distal endthereof capable of preventing or limiting rotation of the jig 454 whenthe fixation member 466 is connected to the pelvis. FIG. 17 shows thatsecuring the jig 462 to the pelvis can include positioning a pin orother bone engaging device through the fixation member 466. The pin andspikes extending from the foot 474 can provide three or more points ofcontact with the pelvis providing secure mounting of the jig 462.

The coupling 475 generally secures the platform 468 to the fixationmember 466. In some embodiment, the coupling 475 has a rotationalcapability that enables the platform to be positioned at selectivelocations about the longitudinal axis of the pin 466, for example toenable the platform 468 to be initially positioned in the correctorientation or to be moved during or after the procedure to make spacefor other surgical devices. One arrangement provides matching splinesthat extend parallel to the longitudinal axis of the fixation member466. This arrangement would permit splines on an upper portion of thecoupling 475 to be disengaged from splines on a lower portion of thecoupling 475. When disengaged, the platform 468 and the upper portion ofthe coupling 475 can be rotated relative to the lower portion of thecoupling 475. The splines can thereafter be re-engaged.

The jig 454 also preferably includes a cradle 476 that can be used tohold a probe arm 477. The cradle 476 includes a U-shaped recess having awidth between two upright members that is about equal to the width of anarm 477 of the landmark acquisition system 462. FIG. 17 shows the probearm 477 in a parked configuration as discussed above. If the sensor 204operates with components that are prone to accumulated error sources,the parked configuration can be used to eliminate such error. Asdiscussed above, the system 450 can be configured such that the positionand/or orientation of the sensor 204 relative to the orientation device172 is known. Thus, when the arm 477 is in the cradle 476 anyaccumulated error of components of the sensor 204 can be eliminated.

The cradle 476 can provide other convenient functions even if thesensing devices in the sensor 204 are not subject to sources ofaccumulated error. As discussed elsewhere herein, for confirmation ofaccuracy of the system or to provide a simplified reference frame notrequiring landmark acquisition, it may be desirable at some point of theprocedure to use the probe arm 477 and the sensor 204 to estimate theplane of the surgical table upon which the patient is resting. If, asdiscussed above, the plane intersecting the slots 470 is orientedperpendicular to the axis of the patient when the jig 454 is mounted tothe pelvis, the cradle will be parallel to the axis of the patient. Ifthe fixation member 466 is oriented vertically, the arm 477 will beparallel to the plane of the table when in the cradle 476. The system450 can thus use the plane of the table as a reference frame for guidingthe placement of the cup without registering landmarks. Or, the plane ofthe table can be used in combination with registering the anatomy aboutthe acetabular rim, as discussed above, to increase the accuracy ofnavigating the cup.

The cradle 476 also provides a convenient home position that keeps thearm 477 stationary and out of the way of other surgical instruments.FIG. 17A illustrates the probe arm 477 withdrawn from the cradle 476 andfree to move into contact with landmarks.

The jig 454 also includes a pivot feature 478 that is disposedhorizontally. FIG. 17B shows that the pivot feature 478 includes twohorizontal apertures 480. One of the apertures 480 is formed in the samestructure forming the cradle 476 but at an elevation below the cradle476. The other aperture 480 formed between the cradle 476 and aprojection of the fixation member 466. FIG. 17A shows that the probe arm477 is connected to the pivot feature 478 by a shaft 482 that extendsthrough the apertures. A movement device is provided between the shaft482 and the arm 477 to enable a distal tip of the arm to be rotatedabout perpendicular axes and to be advanced linearly relative to thestationary jig 454. One axis of rotation A of the movement device isdisposed parallel to and at an elevation above the platform 468. Anotheraxis of rotation B is disposed generally perpendicular to the axis A.Sliding of the arm 477 is enabled by a snug but sliding fit of the armin a housing C. By orienting the axis A in this manner, the sensitivityof accelerometers in the sensor 204 to small angular motions referencespoints about the acetabulum is heightened or maximized. This can enablelandmark acquisition with the system 450 based solely on accelerometers,which advantageously are not subject to accumulated error, which cansimplify the landmark acquisition process. Further variations of systemsthat are configured to allow landmark acquisition based solely onaccelerometers are discussed below in connection with Figures *.

The registration feature 473 is a convenient way to enhance the accuracyof the sensor 204. In particular, in one variation of the methoddiscussed above, a distal tip of the probe arm 477 is brought intocontact with the registration feature 473. In one embodiment, theregistration feature 473 is a notch configured to receive andtemporarily retain the tip. Thereafter, the user can interact with theorientation device 172 to initialize accelerometers within the sensor204. Thereafter the points to be acquired can be sequentially contactedand the orientation and position of the sensor 204 can be sequentiallyrecorded in the system 450. Because the accelerometers are initializedclose to the points to be acquired, accuracy of the reading is enhancedas the angular error resulting from an error in the scale factor of theaccelerometers is minimized due to the small arc from the registrationfeature. For example, the jig 454 is configured to enable the landmarkacquisition assembly 458 to reach all points to be registered by movingless than about 45 degrees from an initial or home position in someembodiments. In other embodiments, the jig 454 is configured to enablethe landmark acquisition assembly 458 to reach all points to beregistered by moving less than about 25 degrees from the initialposition. In other embodiments, the jig 454 is configured to enable thelandmark acquisition assembly 458 to reach all points to be registeredby moving less than about 15 degrees from the initial position.

The jig 454 also is configured to interact well with the soft tissuethat is disposed around the surgical site in the posterior approach. Inthis approach, an incision is made in soft tissue that is kept as smallas possible. In one approach, the fixation member 466 is positioned atthe end of the incision. Where the incision is made as minimal aspossible, the jig 454 can also function as a retractor. The T-shapedconfiguration is particularly well suited for this function because thefirst portion 468A of the platform 468 can be received between themiddle and ring fingers of the user with the second portion 468B in thepalm of the hand. With the foot 474 gripping the pelvis, the jig 454 canbe tilted from the platform 468 away from the hip joint to retract thetissue away.

FIGS. 17C-1 and 17C-2 illustrate further embodiments of a posteriorapproach jig 454A having a mounting device 488 disposed adjacent to thedistal end of a fixation member 466A, which is otherwise similar to thefixation member 466. The fixation member 466A includes a tubular body490 coupled with the fixation member 466A, which in this embodiment actsas a primary fixation member. The tubular body 490 extends along a lumenthat is angled relative to the lumen of the fixation member 466A. Thelumen in the tubular body 490 is configured to accept a fixation pin 492that can be driven into the bone, as illustrated in FIG. 17C-2 at anoblique angle. The fixation pin 492 supplements the fixation provided bythe fixation member 466A. The fixation pin 492 can be used inconjunction with the optional long pin(s) extending through the channels471, e.g., into the ilium or as a substitute for that option. Thefixation pin 492 has the advantage of not requiring any additional holesin the skin because it is located within the primary incision made toaccess the joint in the procedure. The fixation pin 492 can be threadedto engage the bone in one embodiment. In some embodiments, a lockingdevice 494 can be provided to secure the pin 492 in the lumen of thetubular body 490. A set screw is one example of a locking device 494that can be used. The locking device 494 enables the fixation pin 492 tobe headless, which avoids issues with screw threads stripping the holein the bone into which the pin 492 is inserted.

3. Workflow Considerations for Posterior Approach

As noted above, a workflow problem arises in typical hip replacementprocedures in that anatomical features that can be more easilyreferences are unavailable in the traditional posterior approach foroperating on the joint.

By performing a CT-based study of a large number of human pelvises, theassignee of this application has been able to calculate apopulation-based average relationship between multiple planes created byvarious points in, on or around the acetabulum that are accessibleduring posterior approach hip replacement (each plane, an “AcetabularPlane”), and the Anterior Pelvic Plane. One of the key features ofposterior hip navigation for some embodiments disclosed herein is theability of a module, e.g., software incorporated into a processor, whichmay be on a computer, or one or both of the orientation device 172 andsensor 204, to calculate a transformation from one reference frame toanother. As described in more detail elsewhere herein, several pointsare referenced in, on or around the acetabulum and from these points aproxy Acetabular Plane is calculated.

Next, in certain embodiments described herein a module operable toprocess an algorithm, e.g., by executing software in one or both of theorientation device 172 and sensor 204 alone or with a separate computer,is able to calculate a transformation from the proxy Acetabular Plane toAnterior Pelvic Plane. The approach indirectly registers the AnteriorPelvic Plane without requiring a direct supine registration andsubsequent patient movement and re-draping necessary in standardnavigation. A module in certain embodiments described herein is thenable to provide the user real time navigation data of the orientation ofa hip instrument (e.g., the impactors 300, 300A) with respect to theAnterior Pelvic Plane.

In certain systems described herein, a further advantage is that thesystems are able to implement the plane transformation algorithm tocalculate an Anterior Pelvic Plane from one of any number of proxyAcetabular Planes that the surgeon chooses to register. This enables thesurgeon to have greater flexibility in Acetabular Plane landmarkselection to take into account the quality or accessibility of certainlandmarks. For example, in cases of minimal deformity around theacetabular rim, the surgeon may choose to register landmarks around therim, which are easily accessible. In cases where there is greatdeformity or high presence of osteophytes on the acetabular rim, thesurgeon may instead choose to register an Acetabular Plane based onextra-acetabular landmarks (or described as “off-rim” elsewhere herein)outside of the rim that are unaffected by disease or prior hipreplacement surgery.

Examples of anatomical landmarks that may be used to create a proxyAcetabular Plane and that are shown in FIG. 2 include but are notlimited to:

Extra-acetabular landmarks (Ischium/Ilium/Pubis)

(A) The lowest point of the acetabular sulcus of the ischium

(B) The prominence of the superior pubic ramus

(G) The confluence of the anterior inferior iliac spine (AIIS) and theouter border of the acetabular rim

Acetabular Rim Landmarks

(E) The center of the anterior insertion of the trans-acetabularligament

(F) The center of the posterior insertion of the trans-acetabularligament

(H) The most superior point of the acetabular rim.

Additional points can be combined with either of the groups of pointslisted above. For example, in one embodiment, point “D” is used. Point Dis the midpoint of the inferior border of the acetabular notch. Asdiscussed in connection with FIG. 36 below, point D corresponds to thebottom landmark 380B used to form the line 382. Point D is used in thatapproach to provide patient specific refinements to the positioning.

A further key benefit of certain embodiment discussed herein is that theforegoing plane transformation capabilities increase the accuracy of thetransformation between the proxy Acetabular Plane registered and theAnterior Pelvic Plane above the general population average data by theuser inputting certain patient-specific information, such as gender.

Additionally, certain embodiments of systems including one or more ofthe orientation device 172, sensor 204, or a separate computer may havemodules that are operable, e.g., by processing software, to allow theuser to input an angular or plane relationship between an proxyAcetabular Plane and Anterior Pelvic Plane that the surgeon measuredbased on pre-operative imaging, allowing for a partial or whole planetransformation based on patient-specific data rather than populationdata. By way of example, the surgeon may choose to pre-operativelymeasure an angle created by (a) landmarks that are both visible on anA/P pelvis x-ray and that can be referenced during posterior hipreplacement, and (b) landmarks that are both visible on the pelvis x-rayand that are directly associated with inclination measurement in theAnterior Pelvic Plane. If this angular relationship is inputted into amodule of a system including one or more of the orientation device 172,the sensor 204, or a separate computer, which module is capable ofmaking calculations processing software and the surgeon registers thelandmarks described in (a), inclination navigation will be basedspecifically on that patient rather than a population average. Landmarks(D) and (H) listed above are examples of landmarks that are both visibleon an A/P pelvis x-ray and that can be referenced to create a proxyAcetabular Plane in posterior hip replacement.

These aspects of the systems adapted for posterior approach hip jointreplacement can greatly enhance both workflow and accuracy in suchprocedures.

B. Navigation Using Inertial Sensors and Jigs for Referencing AnatomicalLandmarks with Anterior Approach

1. Apparatuses for Anterior Approach Hip Navigation

FIGS. 18-21 illustrate a hip navigation system 500 adapted to navigate ahip joint procedure from an anterior approach. Anterior approach to hipreplacement advantageously can be less invasive than posterior approach.In particular, the anterior approach can enable smaller incisions, lesssoft tissue dissection, and shorten recovery time for patients. Thesystem 500 includes an anchor system 504, an alignment assembly 508 anda landmark acquisition assembly 512.

FIG. 18 shows the anchor system 504 in more detail. The system 504 isconfigured to securely couple the navigation system 500 to the hip, suchthat movement between the system and the hip are minimized oreliminated. The anchor system 504 includes a cannula 516 having a distalend 520 and a proximal end 524 with a lumen 532 extending between thedistal and proximal ends. The proximal end 524 of the cannula 516 iscoupled with a platform 536, for example adjacent to one lateral end ofthe platform. The platform 536 is similar to those hereinbeforedescribed having a plurality of docking device 538, 538A disposed awayfrom the location where the proximal end 524 and the platform 536 areconnected.

The docking devices 538 are configured to couple with detachablemounting devices that securely but temporarily couple sensor to theanchor system 504. The two docking device 538 on the top surface of theplatform 536 enable the anchor system 504 to be used for either left orright hip procedures. As shown in FIG. 18, the docking device 538 on theside of the platform 536 closest to the medial plane of the patient ispreferably used for docking. The top side docking feature not in use inFIG. 18 would in fact be used in performing a procedure from the otherside of the patient. The docking device 538A on the side surface of theplatform 536 is provided for a temporary intra-procedure mounting of asensor to the platform 536. As discussed further below, this temporarymounting provides a known orientation and/or location of two sensorsrelative to each other during a procedure, which enables the system 500to control sources of error with certain types of sensors.

The platform 536 also can have a channel 540 disposed away from thecannula 516. The channel 540 can have a lumen disposed along an axissubstantially parallel to the lumen 532 of the cannula 516. In oneembodiment, the anchor system 504 is configured to securely couple theplatform 536 to the hip by placement of two spaced apart pins 544A,544B. FIG. 18 shows that the pin 544A can be advanced through thecannula 516 such that a distal end of the pin 544A contacts andpenetrates a bony prominence of the pelvis. In one technique the pin544A is positioned at or as close as possible to the anterior superioriliac spine (ASIS) of the pelvis. The pin 544B is advanced through thechannel 540 and into the pelvis at a location offset form the ASIS. Thedistance between the pins 544A, 544B and the precise positioning of thepin 544B are not critical, but are determined by the locations of theconnection of the cannula 520 to the platform 536 and of the channel540.

The pins 544A, 544B can take any suitable form but preferably have thesame cross-sectional profile as the lumens in the cannula 520 and in thechannel 540, e.g., they can be circular in cross-section. The pins 544A,544B can be modified Steinmann pins, e.g., configured to extend at leastabout 5 cm above the platform 536 and having a diameter of about 4 mm.

The anchor system 504 also has a locking device 556 for securing theplatform 536 to the pins 544A, 544B. In one embodiment, the portion ofthe platform disposed around the pins comprises medial and lateralportions 560M, 560L that can move away from each other to release thepins 544A, 544B or toward each other to frictionally engage the pins.For example, a pair of hex-driven screws can engage the medial andlateral portion 560M, 560L to translate them toward and away from eachother respectively. The locking device 556 preferably is quickly andeasily removed from the pins such that other instrument, such as X-Rayor other diagnostic devices can be brought into the vicinity of thesurgical field during the procedure. Preferably the pins 544A, 544B havemarkings along their length such that if the platform 536 is removed forimaging or other reasons it can be quickly re-positioned at the sameelevation.

The cannula 520 also has a foot 568 adjacent to or at the distal end 528to minimize or eliminate error that could arise due to unevenpenetration depth of the anchor system 504 when compared to the positionof a distal probe of the landmark acquisition system 512 when landmarksare being acquired. The foot 568 can include an annular projectiondisposed outward of the cannula 520. Preferably the foot 568 extendslaterally from the outer surface of the cannula 520 by a distance equalto or greater than the wall thickness of the cannula 520. In someembodiment, the surface area beneath the foot is equal to or grater thanthe surface area of the cannula when viewed in cross-section at alocation where the foot 568 is not located, e.g., at an elevation aboutthe foot 568.

The alignment assembly 508 is similar to those hereinbefore described.It can have a rigid extension 570 configured to detachably secure aorientation device 172 to the docking device 538.

The landmark acquisition assembly 512 is similar to those hereinbeforedescribed, but is configured to be unobstructed in use by soft tissueanterior to the pelvis of the patient. In one embodiment, an extension578 is provided to elevate a pivoting and sliding mechanism 582. Thepivoting and sliding mechanism enables a probe arm 584 to slide awayfrom the extension 578 toward the location of landmarks to be acquired.The pivoting and sliding mechanism 582 can be similar to any of thosediscussed above. The distal (lower) end of the extension 578 can becoupled to the platform 536 in any suitable way. For example, the distalend can include a pin-like projection that is received in, e.g.,friction fit in, an aperture 578A having the same shape. Detents orother locking features can be provided to securely connect the extensionto the platform 536 in the aperture 578A. FIG. 19 shows that theaperture 578A can be formed in a portion of the platform 536 that iselevated compared to the portions of the platform through which the pin544A extends. This portion is elevated to provide sufficient bearingengagement to minimize play. It also has a slot generally parallel tothe top surface of the platform 536 which serve the function of engaginga ball detent on the lower end of the extension 578.

The probe arm 584 can be configured as an elongate member with aplurality of markings, discussed below. A distal end of the probe arm584 can include an angled tip 586 that assists in probing anatomy insome techniques, e.g., portions of the femur for leg length and femoralhead positioning confirmation. In the posterior approach, the angled tip586 is used to directly contact anatomy.

In the anterior approach, the angled tip 586 is coupled with a probeextension 590 configured to contact selected anatomy. The probeextension 590 has an upright member 592 that is configured to extend, inthe anterior approach, between the elevation of the probe 584 downtoward the elevation of the tissue to be probed. A foot 594 on thedistal (lower) end of the upright member 592 is configured to engage thetissue in a way that minimizes error due to uneven tissue compressionbetween the point of mounting of the pin 544A and the foot 594. Forexample, the foot 594 can have a cross configuration that spreads outthe force or pressure applied by the landmark acquisition system 512 inuse. The proximal end of the extension 590 includes a coupler 596 thatconnects a distal end of the probe arm 584 with the upright member 592.Preferably the coupler 596 is easily manipulable by the user to modifyconnect to the probe arm 584. The coupler can include an L-shaped memberwith an aperture configured to receive the tip 586 of the probe arm 584.A set screw can be advanced through the L-shaped portion to lock the arm584 in place. The L-shaped portion is configured to couple to the arm584 such that the tip of the angled tip 586 rests on a projection of thelongitudinal axis of the upright member 592.

2. Example Methods for Navigating Using the Anterior Approach

The system 500 can be used to navigate from an anterior approach in thefollowing ways. The orientation device 172 and the sensor 204 can bepaired such that they are in wireless communication with each other.This permits one or other of the device 172 and sensor 204 to controlthe other, store data from the other, and/or display information basedon signals from the other. In one method, the orientation device 172 hasa display that confirms to the surgeons certain angles based on the datasensed by the sensor 204. The pairing the device and sensor 172, 204 caninvolve coupling them together and comparing sensor output between thetwo devices at a plurality of orientations, e.g., horizontal, vertical,and angled at 30 degrees. Some of these positions may be repeated with aplurality of attitudes, e.g., vertical with left side up, vertical withright side up, and vertical with top side up.

As noted above, the components discussed herein can be provided as a kitthat enables the surgeon to select among different surgical approaches,e.g., posterior and anterior approaches. The orientation device 172 andsensor 204 may operate differently in these different approaches. Thus,in one method the user will enter into one or both of the orientationdevice and sensor 172, 204 which approach is being used. This willimplement a software module in the orientation device 172 (or in thesensor 204 is the processor running the software is located there)corresponding to the selected approach.

In various embodiments suitable for the anterior approach, theorientation device 172 and the sensor 204 can both have a plurality ofsourceless sensors. These components can have both accelerometers andgyroscopes in some embodiments. Some gyroscopes are subject toaccumulated error that can be significant in the time frames relevant tothese methods. Accordingly, various methods are provided to prevent sucherrors from affecting the accuracy and reliability of the anglesdisplayed to the surgeon by the system 500. Some approaches can beperformed with accelerometers only. For example, variations of theanterior approach can be performed with accelerometers with somewhatless but still acceptable accuracy using accelerometers only. Thereduction in accuracy of the accelerometers is balanced against thebenefit of eliminating the accumulated error that arises with somegyroscopes. The resolution of accelerometers is sufficient because thepoints navigated are relatively far apart.

The calculations performed by the system 500 are unique to the hip beingtreated in some embodiment, so the system receives input of the hipbeing treated.

The foot 568 is placed on a selected anatomical location, e.g., on theASIS as discussed above. With the cannula 520 in an approximatelyvertical orientation the platform 536 is secured to the hip. Securingthe platform 536 to the hip can be done in any suitable way, such aswith two spaced apart Steinmann pins. Thereafter, the orientation device172 and the sensor 204 are attached to the platform 536 in the mannershown in FIG. 20A. Depending on the nature of the sensing devicesdeployed in the sensor 204 it may be advantageous to initialize thesensor at this point of the procedure. As discussed above, certaininertial sensors (e.g., some gyroscopes) are subject to accumulatederror. One technique for managing this error source is to periodicallyinitialize or zero out this error. Some techniques involve initialing atthis point.

In some embodiment, a frame of reference based on the plane of the tablecan be input into the system 500. The table reference frame can be asecondary reference frame. In one technique, the sensor 204 is movedfrom the platform dock position of FIG. 20A to the navigating positionon the probe arm 584 as shown in FIG. 18. The probe arm 584 is thenpivoted by the mechanism 582 such that the arm points in a directionthat is parallel to the patient's medial-lateral mid-plane and theangled tip 586 superiorly (generally toward the patient's head). Theprobe arm 584 is also held substantially parallel to the plane of thetable. With this heading and orientation the user interacts with a userinterface on the orientation device 172 to signal to the orientationsystem 508 to capture the orientation of the sensor 204. Thisorientation provides an estimation of the orientation of the anteriorpelvic plane. This estimation may be tracked in the system 500 and mayalone provide an improvement over the state of the art in un-navigatedhip replacement, which involves discrete maneuvers guided by the unaidedeye.

At the surgeon's discretion the system 500 can be used to navigate acondition of the femur prior to hip replacement. A mark Fm may be madeon the proximal femur. Thereafter the sensor 204 can be initialized orzeroed such as by placing it back in the dock position on the platform(as in FIG. 20A). Thereafter, the probe tip 586 can be brought intocontact with the femur mark Fm and locked in place in such contact. SeeFIG. 21A. The sensor 204 can be transferred to the proximal end of theprobe 584 and the orientation device 172 can be signaled to record theorientation of the sensor 204. A distance from the point of attachmentof the cannula 520 to the ASIS to the marked position on the femur canthen be recorded in the orientation device 172. The position can bebased on reading graduated marks on the probe 584 or can be capturedautomatically by a camera system or a sensor built into the system 500.In one embodiment, graduated marks are read at an upright edge 598within a bight of a sliding portion of the pivoting and slidingmechanism 582.

FIG. 20A illustrates a further step of navigating the anterior pelvicplane. As shown, the sensor 204 is docked on the platform 536, in whichposition any accumulated error associated with some sensors can beeliminated. In a preceding step, the extension 590 is coupled with thedistal portion of the probe 584. The foot 594 is brought into contactwith the contralateral ASIS. Thereafter, the sensor 204 can be attachedto the proximal end of the probe 284 as shown in FIG. 18. The landmarkacquisition system 512 can be immobilized and the orientation of thesensor 204 can be recorded in memory in the orientation device 172.Additionally, the distance that the probe 584 is extended to contact thecontralateral ASIS can be recorded in the orientation device 172. Asnoted above, that distance can be read from the scale on the probe 584at the upright edge 598.

The process to record the contralateral ASIS can be repeated for one ormore additional points. The sensor 204 can be docked to the platform asin FIG. 20A to eliminate sources of accumulated error. The probe 584 canthen be moved to cause the foot 594 to be in contact with a pubictubercle. The probe 584 can be immobilized and the sensor coupled withthe proximal end as shown in FIG. 20B. Thereafter data indicative of theorientation of the sensor 204 and the distance to the pubic tubercle arerecorded in the orientation device 172 in any of the manners discussedabove.

Once the foregoing points of the pelvis have been navigated and the datarecorded into the orientation device 172 the anterior pelvic plane canbe calculated from data indicating the navigated points. The orientationof the anterior pelvic plane is a baseline for placement of the cupportion of a hip prosthesis.

The sensor 204 and the orientation device 172 can at this point be usedto guide placement of the cup 360 in the prescribed orientation. Priorto placement the impactor 300, 300A is provided. For example, theimpactor 300A can be provided by selecting the appropriate tip component348 onto the distal end of the shaft 316A. The tip component 348 iscoupled with the cup 360, e.g., by threads. The rotational orientationof the cup 360 to the shaft 316A that is most convenient given holepatterns and position of the sensor 204 is selected by matching up theflats 350A, 350B as appropriate. During the process of providing theimpactor 300 the sensor 204 can be docked to the platform 536 and sourceof accumulated error can be eliminated just prior to navigating the cup360 into place in the acetabulum.

In one technique, the cup 360 is inserted into the acetabulum and placedto approximately the correct orientation. Thereafter the sensor 204 isconnected to a docking device 338 on the impactor as shown in FIG. 11A.The orientation device 172 is the activated to display angles indicativeof the orientation of the cup, e.g., degrees of inclination andanteversion with respect to the anterior pelvic plane. The angledisplayed can directly reflect the table reference frame discussedabove. The angle displayed can directly reflect the frame of referencefrom the acquisition of landmarks. In some cases, angles can bedisplayed that directly reflect both table reference frame and landmarkreference frame. In other embodiments, the table reference frame is notdisplayed but rather causes a user instruction to be displayed on theorientation device 172, such as a direction to re-acquire landmarks dueto disagreement between the angles generated by the two referenceframes.

Any of the foregoing combinations of table and landmark reference framesprovides redundancy that ensures that the angle information provided tothe user is accurate and reliable such that the procedures performedwill be better contained within the “safe zone”.

When the correct angles are achieved, a tool is used to strike theproximal end of the impactor 300 to lodge the cup 360 in place at thedesired angle. In some techniques, the sensor 204 is removed prior tostriking the proximal end of the impactor 300. The system 500 includes amodule that monitors signals from the sensor 204 and if a largedeviation in the readings occurs, the module prevents the angles on thedisplay of the orientation device from changing. This “freezing” of thedisplay is both a safety and an accuracy precaution because a largeforce due to impact can affect the accuracy of the sensor 204.

If femoral landmarks are acquired in the procedure prior to separatingthe natural joint, the same landmarks can be acquired after theprosthetic joint is placed to confirm that the replacement of the jointhas not changed either the length of the leg, the off-set of the legfrom the trunk of the patient or both. For example, the sensor 204 canbe docked to the docking device 538A as shown in FIG. 20A. Sources ofaccumulated error can be eliminated by initializing the sensor 204.Thereafter, the probe arm 538 can be brought into contact with the samelandmark (e.g., Fm) acquired early in the procedure. See FIG. 21B. Theprobe arm 538 can be locked into place and thereafter the sensor 204 canbe coupled with the proximal end of the probe arm 538. The orientationof the sensor and the distance to the probe arm 538 can be input intothe orientation device 172. These data enable the orientation device 172to output amounts of change in leg length and leg offset.

In one variation a plurality of points, e.g., three points, on the femurare acquired before and after the joint is replaced. This approachenables a further confirmation that the rotation orientation of the neckof the femur relative to an axis extending through the center of the cup360 perpendicular to the plane of the acetabulum is unchanged after theprocedure.

Of course, the femur registration procedures enable correction ofdiagnosed deformities including excessive leg length offset and jointoffset, as well as mal-orientation of the femoral neck in the naturaljoint. In other words, the surgeon can begin the procedure with theintent of adding some offset or changing rotational orientation toimprove the patient's bone positions and/or orientationspost-operatively.

C. Navigation Using Pre-Operative Imaging or Characterization

Although the foregoing approaches can improve the standard of carecurrently in place, further increases in accuracy and even betteroutcomes and streamlining of the procedure can be provided if the systemis configured to account for patient specific anatomical variability.

1. Navigation Using Inertial Sensors and a Custom Jig

FIG. 22 shows the placement of a hip movement tracking sensor 204 on apin 732 adjacent to the acetabulum. This position is not limiting, inthat the hip movement tracking sensor 204 can be mounted anywhere on thepelvis, but adjacent to the acetabulum is convenient. The pin 732 hasbeen placed with the aid of a pre-operative characterization of the hipof the specific patient. In these methods the pin 732 is placed withoutthe need for intra-operative landmark acquisition.

In one approach, a pre-operative three-dimensional characterization ofthe acetabulum is performed using any suitable technology, such as CTscan or MRI. This pre-operative procedure can be performed to fullycharacterize the pelvis and, in some cases, the proximal femur.Thereafter, the shape, location and orientation of the acetabulum areknown. Also, the bony features around the acetabulum are known. Fromthis data, a custom jig 700 can be fabricated specific to the patient.The custom jig 700 not only has features that are specific to theindividual patient's anatomy but also a registration feature 702 thatwill be at a known orientation to the plane of the acetabulum and to theanterior pelvic plane.

FIG. 23 shows an example of the custom jig 700. The jig 700 has ananterior side 704 and a posterior side 708. The posterior side 708 isformed with an acetabular portion 712 configured to mate with at leastone feature of the acetabulum in a secure manner. For example, theacetabular portion 712 can fit snugly over the acetabular rim with acentral portion of the posterior side 708 positioned in the acetabulum.The jig 700 preferably has only one pre-defined orientation. A surfaceon a posterior portion of the jig can define a plane that corresponds toa preferred orientation angle of the cup post-implantation. One or morechannels 716 can be formed on the posterior side 708 that receive thelocal bony prominences of the acetabular rim only when the jig 700 is inthe proper position and orientation. In another approach, theregistration feature 702 of the jig 700 has a face or a hole that isoriented in the desired orientation for the shell or cup of the implant.Thus, once the jig 700 is placed, the sensing device 204 can bepositioned against the face or surface or, if coupled with a pin 732,the pin can be inserted into the hole. From the orientation of thedevice when so placed, the orientation of the acetabular rim or a proxythereof can be recorded in one or both of the devices 172, 204. The hole702 preferably extends from the anterior side 704 to the posterior side708 of the jig 700. The distance between the anterior and posteriorsurfaces 704, 708 provides the depth of the hole 702 being sufficient toguide a pin to specific anatomy along a specific direction.

FIG. 24 shows initial placement of the jig 700 in the acetabulum in anorientation dictated by the fit of the jig 700 over the anatomy. Theprofile of the posterior side 708 including the channel(s) 716 receivesthe specific patient's acetabular rim including local prominences andrecesses of the bone at and around the acetabulum. The hole 702 islocated on a peripheral projection 720 of the jig 700. The configurationof the projection 720 is such that the hole 702 is disposed over aspecific bone or bone region of the hip. In this example, the projection720 is configured to be disposed over the bone superior to theacetabulum. Other regions of bone around the acetabulum can be used ifsufficiently thick or strong and in a convenient position to not blockactions of the surgeon during the procedure. The precise location of theprojection 720 chosen can be determined by the pre-operative imaging andfactored into the forming the custom jig 700.

FIG. 25 shows that after the jig is placed the pin 732 can be placedthrough the hole 702. The pin 732 has a length that extends above theanterior surface 704 of the jig 700 such that the sensor 204 can bemounted thereto. Once the sensor 204 is mounted to the pin, the sensorcan track any movement of the pelvis during the procedure. There is noneed for registration of landmarks in this technique because theposition and orientation of the pin relative to the acetabulum and/or tothe anterior pelvic plane are known from the pre-operative imaging.

FIG. 26 shows that the plug 700 advantageously can include an alignmentguide 736 to control rotational orientation of the sensor 204 on the pin732. The alignment guide 736 can be a line extending along a specificdirection relative to the registration feature 702. As noted above, thesensing devices inside the sensor 204 can be sensitive to the directionof gravity. Tilting of the sensor about the pin 732 can change thereadings of these sensing devices. To eliminate sources of errorassociated with this sensitivity, the navigation system incorporatingthe sensor 204 can be programmed to assume that the sensor will be at aspecific rotation position about the longitudinal axis of the pin 732.The sensor 204 may be mechanically or visually aligned with the guidingmark 738 to assure that this assumption is met in use. In one variation,the sensor 204 has a laser that projects onto the jig 700 and can bealigned with the mark 736 to facilitate alignment. Alternatively, thepin 732 may be configured to only enter the hole in a unique orientation(for example, with an asymmetric non-circular cross-section), and toallow the sensor to mount to the pin in a unique orientation (byincluding asymmetric coupling features).

Once the sensor 204 is mounted to the pin 732, the jig 700 can beremoved from the surgical area. For example, the jig 700 can be made ofmaterial can be cut along a line 742 in a lateral edge of the jig. A sawor rongeur can be used to cut through the jig 700. Thereafter, themajority of the body of the jig 700 can be removed from the surgicalarea. FIG. 28 shows that in some methods, the projection 720 is left inplace so that the position and orientation of the sensor 204 is notdisrupted.

A second sensor 204 is attached to a cup impactor, which may be the sameas in FIGS. 11A-11C. The impactor guides the placement of the cup withreference to the signals from the sensor 204 mounted on the pin 732 onthe pelvis. Signals from the sensor on the impactor can be corrected ifmovement of the hip is detected by the sensor on the pin 732.

2. Navigation Using Inertial Sensors and a Cannulated Guide

FIGS. 29-31 illustrate one way of implementing cannulated guide deliverymethods. Cannulated methods are advantageous in that once a guide memberis mounted, the tracking of orientation is simplified and may no longerbe necessary in some cases, which can eliminate accumulated errors,sensor drift, or erroneous readings of other sorts as a concern.

A custom jig 750 is formed by the process discussed above in connectionwith the jig 700. The jig 750 has many of the same components as thoseof the jig 700, including a registration feature 752 extending betweenthe anterior and posterior surfaces 754, 758. A guiding mark 738 can beprovided on the anterior surface 754 to align the sensor 204rotationally about the pin 732. The jig 750 also has a guide channel 762located generally centrally in the jig 750. The guide channel 762 has ananterior opening on the anterior surface 754, a posterior opening on theposterior surface 758, and a wall extending between these openings. Thewall is disposed about a central axis A. The position and orientation ofthe axis A can be determined based on the pre-operative characterizationof the acetabulum. In one embodiment, an MRI or CT scan reveals anoptimal axis for delivering a prosthetic cup along. The wall forming theguide channel 762 is formed about the axis A which coincides with thisoptimal axis when the jig 750 is placed on the specific patient'sacetabulum.

FIG. 30 shows that the impactor 300A can then be advanced along the axisA into the guide channel 762. A distally facing shoulder 766 on theimpactor 300A can mate in a pre-defined way with the anterior surface754 and the entrance to the channel 762 and when so mated theorientation of the sensor 204 on the impactor 300A can be recorded. Inthis technique, the jig 750 is a cannula with the channel 762 configuredto receive the impactor 300A. If patient movement is possible, thesensor 204 on the pin 732 can be retained in place to track suchmovement. If not, the sensor 204 on the pin 732 can be removed. Thesensor 204 on the impactor 300A will have stored the orientation of theaxis A in memory and will be able to inform the user of any variance ofthe impactor from this axis. It is preferred to retain the sensor 204 onthe pin 732, as the orientation can only be accurate stored by thesensor 204 on the impactor 300A for a short time due to accumulatederror (e.g., drift) of some sensors, e.g., some lower cost gyroscopes.

In one variation, the impactor 300A has a central channel that coincideswith the axis A when the impactor is placed into the guide channel 762and the shoulder 766 abutted with the surface 754. A guide pin can beadvanced through this channel and into the acetabulum. The guide pin canbe lodged in the base of the acetabulum. The sensor 204 coupled with thepelvis by the pin 732 can be removed because the guide pin placedthrough the channel of the impactor 300A provides a mechanical way oftracking movement of the hip. Thereafter the impactor 300A with the cupmounted thereon can be slide over the guide pin and into place in theacetabulum.

In a further variation, the sensor 204 coupled with the impactor 300Acan also be removed. In this further variation, the guide pin isconfigured along with the cup to prevent tilting of the prosthetic cuprelative to the axis A. In particular, an interface between the guidemember and the cup of the hip prosthesis could be made to havesufficient length along the axis A that tilting is prevented by thisinterface. In some cases, the cup 360 is coupled to the impactor 300,300A. A variation of the impactor 300, 300A can be tubular or haveanother feature for interfacing with, e.g., tracking along the guide pinin the pelvis.

3. Navigation Using Inertial Sensors and Pre-Operative Imaging

In another technique using less comprehensive imaging, a correspondencebetween one or more linear dimensions and an angle can be exploited toenhance accuracy. For example, a clinician can use an X-ray or otherstandard radiographic imaging device to provide an anterior pelvic boneimage. This image can be read to derive the location of the anteriorpelvic plane and a dimension on the anatomy. For example, an anglebetween top and bottom landmarks around the acetabulum (as furtherdescribe below) and a trans-ischial line or other anatomicmedial-lateral reference line can be a useful patient specific variableto minimize patient-to-patient variation in at least one relevant angle,e.g., the abduction angle.

Patient specific data can be provided for use by the surgeon based onbest medical judgment. For example, any of the systems herein can beused in a mode that is based on broad population studies. Such studiescan define a distribution of patients with sufficient clarity and detailto enable significant improvement over the current standard of care. Inone mode, the dimensions taken from radiograph or CT can be used toinform the surgeon whether some patient specific adjustments should beconsidered. Alternatively, patient specific adjustments can be codedinto the system 100 so that they are transparent to the doctor. Suchadjustments can be downloaded to either or both of the devices 172, 204or into a separate monitor or control device that communicateswirelessly with the devices 172, 204. Thus, the system 100 can eitherfully implement patient specific adjustment, e.g., for anteversion,abduction, leg length, joint offset, or other parameter or can enablethe surgeon to make a judgment as to whether to do so.

FIG. 36 illustrates an example of a pre-operative image that can be usedin one technique. The lines 380 point to landmarks which are usedintraoperatively and are also visible in an anterior pelvic radiograph.The top landmark 380A is about 1 cm superior to most superior point ofacetabulum. In another approach, the top landmark 380A can be the mostsuperior point on the acetabular rim. The bottom landmark 380B isadjacent to or at the acetabular notch (tear drop). An angle betweenline 382 and the line 384 is a patient-specific abduction of line formedby landmarks, which can be entered into an interface of the system 100(or the other systems herein) at time of surgery to provide patientspecific reference frame. Line 384 may be any anatomic medial-lateralreference line. Examples include trans-ischial line and line across theinferior borders of the obturator foramina (shown in FIG. 36).

4. Navigation Using Drift Insensitive Inertial Sensors

In one variation, one or both of the devices 172, 204 can comprise onlyaccelerometers and can be configured as tilt meters, or the devicescould be put into a mode that relies mostly on the accelerometer data orotherwise be configured to be insensitive to accumulated errors thatarise from integration of data. If the patient is set in a reproducibleand stable position, patient movement and mis-orientation can beeliminated. This enables some methods to be performed without using ratesensor data. In one variation of this tilt-meter approach, one or bothof the sensors 172, 204 can be configured to inform the surgeon if acondition is sensed that suggests a landmark acquisition approach wouldyield a superior alignment outcome. This method can advantageously beused for procedures that do not require complex movements, like freehandmotions. Where freehand motion is involved, incorporating someindication of heading (gyroscopes, magnetometer, or other indication ofheading) would be useful.

5. Navigation Using Inertial Sensors to Track Motion to Define aPatient-Specific Safe Zone

In another technique illustrated by FIG. 32, a patient-specific “safezone” is defined by recording the patient's natural range of motion ofone more of the patient's joints. For example, if a hip procedure is tobe performed, the patient's range of motion can be recordedpre-operatively. If the hip to be replaced is not overly arthritic, therange of motion can be determined on the hip to be replaced. If therange of motion of the hip to be replaced is unnatural due to diseasestate, the contralateral hip can be characterized.

In one hip replacement technique a sensor S is coupled with the femur.The sensor can be coupled above the knee to prevent movements at theknee from affecting the measurements made. The sensor S can be connectedbelow knee if the knee is immobilized. The sensor S can be initializedand otherwise prepared to record accurate readings. Thereafter one ormore movements of the hip joint can be performed with the output of thesensor recorded and processed. The movements can include, for example,movement in anterior and posterior (A-P) directions to the full extentof the range of motion and movement in medial and lateral (M-L)directions to the full extent of the range of motion. These motionsdefine the patient's natural range of motions in these planes.

Based on the extents of motion in the A-P and M-L directions, a cone ofmotion CM can be defined. The cone of motion CM can be defined asoriginating at a point defined as the center of rotation of the femoralhead and extending out from the acetabulum to a circular base located adistance from the center of rotation equal to the distance to the mountpoint of the sensor. The circular base can be defined as having a radiusequal to the average extent of motion in the A-P and M-L directions. InFIG. 32, the cone of motion is shown on the contralateral side forclarity. As noted above, the data collected to estimate the cone ofmotion can be based on the leg to be treated or the contralateral leg.

Placement of the cup of the hip prosthesis is dictated by some metric ofcentering within the cone of motion. For example, the cup can becentered such that an axis extending perpendicular to the plane of theentrance to the cup crosses the circular base of the cone of motionprecise in the center of the cone. In some systems, the orientation ofthe cup is controlled such that the crossing point of the axis soprojecting is closer to the center of the circular base than it is tothe periphery of the circular base. In other systems, the orientation ofthe cup is controlled such that the crossing point of the axis soprojecting is within a distance from the center point that is less than25% of the radius of the circular base.

In a class of patients, the movement of the hip is not symmetrical ineach of the A-P and M-L directions. As such, the cone of motion can havea more complex geometry. For example, the cone of motion can originateat the center of rotation of the femoral head and extend to a basehaving an oblong shape, for example shortened in the medial direction,but longer in the lateral, anterior, and/or posterior directions.Various metrics of “within the safe zone” can be defined based on theseirregular shaped cones. For example the geometric center of a complexbase shape can be calculated and the cup of the prosthetic joint can becentered such that an axis extending perpendicular to the plane of theentrance to the cup crosses the irregular shaped base of the cone ofmotion at or within some maximum distance of the centroid of the cone.

Any suitable set of motions can be used to obtain the center of rotationof the femoral head and/or the boundaries of the base of the cone ofmotion. Examples of methods for determining the center of rotation of afemoral head using inertial sensors are discussed in U.S. Pat. No.8,118,815, which is hereby incorporated by reference for this and allother purposes. A more complete perimeter of the base of the cone ofmotion can be directly recorded using sensors that are capable oftracking both position and orientation. For example, several otherpoints between the A-P and M-L direction can be taken so that six,eight, ten, twelve or more extents are recorded. In other embodiments,arcuate motions of along all or portions of the perimeter of the base ofthe cone of motion can be traced and recorded. Because several degreesof freedom of the sensor S are constrained, the sensor can operate basedon accelerometers only in some approaches, which simplifies sensor S andenables it to be disposable and/or less expensive to make. Suchapproaches may be most accurate if rotations about a vertical axis areminimized or eliminated.

In one embodiment, the procedure illustrated in FIG. 32 generates anorigin and a direction that can be input to a cup placement system. Theorigin can be the center of rotation of the femoral head and thecorresponding center of rotation of a prosthetic socket. The directioncan be a line connecting the origin and the point of intersection withthe base of the cone of motion. This data is transferred to a cupplacement system, such as any of those discussed above. For example, theimpactor 300A can include the sensor 204 to which this data has beensaved. Thereafter movements of the impactor 300A can be tracked withreference to this origin and direction to assure proper placement of thecup. Such placement can be with the aid of a patient movement trackingsensor pinned to the pelvis for example.

In other embodiments, cannulated systems can be used to minimize thenumber of steps during which inertial sensors are used. For example,once the origin and direction of the axis connecting the center ofrotation and the intersection with the base of the cone of motion aredetermined, a guide member can be placed via a cannulated impactor (orother cannula). The guide member can dock with an impactor-mounted cup.The cup can be slid over the guide member into place in the acetabulum.The direction and origin information collected in the steps illustratedby FIG. 32 are preserved by the guide member and by the tilt preventingfeatures on the guide member and/or prosthetic cup.

If the patient's joint is subject to extensive disease, a cone of motioncan be established by a combination of data collected in motions similarto those discussed above in connection with FIG. 32 and pre-operativeimaging. For example, X-rays can be taken when the femoral neck is movedclose to the acetabular rim to supplement some of the data pointsdefining the cone of motion. Thus, the cone of motion can be in partestablished by inertial sensing and in part by imaging to characterizethe native anatomy.

D. Modular System for Anterior or Posterior Approach to Navigation UsingInertial Sensors and Anatomical Landmark Acquisition Jigs

FIGS. 37-40 illustrate a system 900 for navigating a hip procedure. Thesystem 900 can be similar to some of those discussed above. But, whilesome of the foregoing systems are specialized for a particular approach,the system 900 includes a first sub-system 900A adapted for a posteriorapproach and a second sub-system 900B adapted for an anterior approach.As discussed more below, both systems 900A, 900B are configured toenable navigation to be conducted without requiring gyroscopic or othersensors that are subject to accumulated error (drift). This refinementmakes the system simpler to implement and to use in a wider variety ofsettings and with more patients.

The system 900A includes a jig 904A that is adapted for hip jointnavigation from a posterior approach. The jig 904A is similar in somerespects to the jig 454, and any consistent description thereof isincorporated herein. The jig 904A includes a platform 908, a cannulacoupling device 912, and a registration jig mounting feature 914. Theplatform 908 can have any shape, but in some implementations can beelongate, e.g., having a first end 916 and a second end 920. Theelongate shape enables at least a portion of the jig 904A to be lowprofile in one direction and to provide a plurality of positions along alength for coupling devices to the jig. The first end 916 is configuredto be oriented inferiorly and the second end 920 to be orientedsuperiorly when the navigation jig is applied to the patient. Themedial-lateral dimensions or extent can be minimized to not obstruct thesurgical field or the surgeon.

The cannula coupling device 912 is disposed adjacent to the first end916 and is configured to enable a cannula 924 to be held adjacent to abottom surface of the platform 908. The cannula 924 can have a topsurface connected to a bottom surface of the platform 908. A connectionbetween these components can be secured by a device disposed abovewithin or below the platform 908. In one form, a proximal structure ofthe cannula 924 can be received within a bottom recess of the platform908 and can be held within the recess by a compression device, such as aset screw S. Details of several variants of cannula coupling devices 912are discussed below in connection with FIGS. 41-43B. A connection to abone adjacent to a hip joint is made through the cannula 924. Forexample, a pin 928 can be placed through the platform 908 and thecannula 924 into the bone.

An anterior approach cannula 926 is shown in FIGS. 39 and 40 and issimilar to the cannula 516, the description of which is incorporatedherein. The description of the cannula coupling device 912 appliesequally to the cannula 924 for posterior approach and to the cannula 926for anterior approach.

The registration jig mounting feature 914 is disposed on a top surface932 of the platform 908 adjacent to the first end 916. In one form, themounting feature 914 includes an elevated portion of the platform. Themounting feature can include one or more, e.g., two recesses into whichpins can be received. In one embodiment, the elevated portion includes awindow, e.g., a through hole, for viewing such a pin to confirm correctplacement. As illustrated in FIG. 41, in one variant, a circular recesscan be provided for a first pin and an U-shaped slot can be provided foranother pin or member.

The hip navigation jig 904A also includes registration jig 940. Theregistration jig 940 can have some features similar to those discussedabove. The registration jig 940 includes an upright member 942, arotatable member 948, and a probe 952. The upright member 942 isconfigured to be detachably coupled to the platform 908 at theregistration jig mounting feature 914. For example, a plurality of(e.g., two) pins can project from a lower surface of the upright member942, the pins being configured to be received in corresponding recessesin the registration jig mounting feature 914. One of such pins isvisible through the window in the registration jig mounting feature 914seen in FIG. 38. The upright member 942 includes a first portion 944 anda second portion 946 disposed above the first portion 944. The firstportion 944 is substantially vertical and increases the elevation of thesecond portion 946 when the registration jig 940 is mounted to theregistration jig mounting feature 914. The second portion 946 isinclined away from a vertical longitudinal axis of the first portion944. The incline of the second portion 946 provides several advantages.It enables the upright member 942 to be out of the way of the range ofmotion of the probe 952, as discussed below. This is important becausethe probe 952 has to be able to easily and quickly reach a plurality ofanatomical features.

The incline of the second portion 946 also provides a simple way toincline an angle of rotation of the rotatable member 948 relative to avertical axis. The rotatable member 948 is coupled with the uprightmember 942 for rotation about an axis A that is not vertical when thejig is mounted to the bone adjacent to a hip joint and the uprightmember is disposed generally vertically. This arrangement is one way toenable a navigation system employing inertial sensors to eliminate theneed to manage sensor drift. As discussed above, certain sensors, suchas gyroscopes, are more subject to accumulated errors (drift). Theorientation of the axis A enables the jig 904 to be used in a systemthat includes accelerometers and other sensors that are sufficientlysensitive if activated and moved about axes that are not vertical.

As in the registration devices discussed above, other degrees of freedomof rotation and position can be provided in the registration jig 940 andsuch description is incorporated here.

The probe 952 had a tip 956 for engaging anatomy. The anatomy engagingtip 956 is disposed at a distal end of an elongate body 960 coupled withthe rotatable member for rotation about the axis. The orientation andposition of the elongate body 960 of the probe can be adjusted to bringthe anatomy engaging tip into contact with a plurality of anatomicallandmarks during a landmark acquisition maneuver. Such adjustments canbe by sliding through a sliding support, similar to those hereinbeforedescribed.

The upright member 942 can include a cradle 954 that allows the elongatebody 960 of the probe 952 to be held in place when not in use during aprocedure. The cradle 954 can be used to latch the sensor 204, asdiscussed above. In various implementations, the system 900 does notrequire any steps of zeroing, however, since the sensors are configuredto be generally drift insensitive. Eliminating sensitivity to drift canbe achieved by configuring the sensor 204 as a tilt meter, and/or byusing any sort of inertial sensor that will not introduce excessiveerror due to drift during the procedure time. As such, even sensors thathave some drift can be used, so long as their accumulation of error doesnot reach a significant level until during the procedure. The cradle 954could be used to zero error if a procedure was unexpectedly long and thesensor were subject to some drift. In one advantageous embodiment, thesensor 204 can operate solely with signals from accelerometers, whichare insensitive to drift.

FIGS. 37-40 show that the systems 900A, 900B can include one or moresensors for detecting orientation of the probe 952. The sensors can takeany form, e.g., can include the surgical orientation device 172 and thesensor 204 discussed above. Accordingly, the jig 904 can include asensor mounting feature 962 disposed on the platform 908. Where theplatform is elongate, the sensor mounting feature 962 can be disposed atthe second end 920. Another advantage of the jig 904A, 904B is that itis symmetrical and can be used on both hips. The jig 904A, 904B thus canhave a single sensor mounting feature disposed on a plane of symmetry.If the platform 908 is elongate, the sensor mounting feature 962 can belocated on a vertical mid-plane of the platform. Vertical here refers tothe orientation of the jig 904A, 904B when applied to the hip in aposterior or anterior approach.

The registration jig 940 can include a sensor mounting feature 964disposed thereon for movement with the probe 952. For example, thesensor mounting feature 964 can be located at a proximal end of theelongate body 960. This location is one of convenience, placing thesensor 204 at the proximal end. However, the sensor mounting feature 964and the sensor 204 could be located on a side surface of the elongatebody 960.

As discussed herein, the orientation of the axis of rotation A of therotatable member 948 enables the change of orientation of the sensor 204to be other than in the horizontal plane. This is accomplished byorienting the axis A other than in the vertical direction. With thisarrangement, it is possible to configure at least the sensor 204 as atilt meter, e.g., using primarily or only accelerometers to output asignal indicative of orientation of a component, such as of the prove952. Example of angles or ranges of angles of the axis A that can beprovided include about 20 degrees from horizontal, about 30 degrees fromhorizontal, about 45 degrees from horizontal, at less than about 60degrees from horizontal.

FIG. 38 shows a further feature of the system 900A, which includes thejig 904A and the cannula 924. The cannula 924 is adapted for posteriorapproach is similar to or the same as the hollow fixation member 466. Anupper or first end of the cannula 924 is configured to couple with thecannula coupling device 912, such as by a set screw as discussed above.A second end of the cannula 924 is configured to couple with a boneadjacent to the hip joint. The bone can be any of those discussed abovefor coupling the fixation member 466 or other analogous structuresdiscussed in any embodiments above. A home point feature 968 is disposedadjacent to the second (lower) end of the cannula 924. The home pointfeature 968 is in a predefined, known position and can receive theanatomy engaging tip 956 of the probe 952. When these structurescontact, they are in a predefined position and orientation. The homepoint feature 968 can be similar to the registration feature 473discussed above.

Because the system 900 can be adapted for posterior approach or foranterior approach (discussed below), the cannula 924 should be maderemovable from the platform 908 in the operating room or at a back tablein preparation for surgery. As such, the connection between the cannula924 and the platform 908 can be made orientation specific. This reducesa potential source of operator error, i.e., the home point feature 968always faces toward the surgical field from the hip bone attachmentlocation, e.g., faces inferiorly if the jig 904 is mounted to a superiorlocation of the surgical field. For example, a projection on a proximalportion of the cannula 924 and a corresponding projection in a recess onthe lower side of the platform 908 can define only one rotationalorientation of the cannula relative to the platform in which thesecomponents can be coupled.

As discussed above, the cannula 926 is provided in the system 900 toenable a surgeon to switch to an anterior approach. Anterior approach isdiscussed in great detail above, e.g., in connection with FIGS. 18-21B,which description are incorporated here as well. The system 900B differsfrom the system 500 in that the orientation of the axis A of rotation inthe system 900B is not vertical, as discussed above. As such, thesensors can be greatly simplified compared to the system 500. Thecannula 926 has a home point feature 968B. The home point feature 968Bis in a predefined, known position and can receive the anatomy engagingtip 956 of the probe 952. When these structures contact, they are in apredefined position and orientation. The home point feature 968B can besimilar to the registration feature 473 discussed above. The cannula 926and the platform 908 can be configured for limited, e.g., only one,rotational position of attachment. This assures that when the jig 904Bis assembled in the operating room or back table that the jig 904B willbe properly set up.

In one method to maximize the accuracy of the landmark acquisition, jig904B is coupled with the patient in an anterior approach. The tip 956 isput into contact with the home point feature 968B. Thereafter, userinput can be applied to the surgical orientation device 172A to indicatethat the tip 956 is in the home point feature 968B. Thereafter, thesystem registers movements and landmark acquisition in the mannerdiscussed above. These data provide a basis to guide the placement ofthe acetabular cup, as discussed above.

The placement of the acetabular cup using a device such as the impactor300A can be an operation that benefits from inertial sensors that mayinclude one or more drift-sensitive sensors, e.g., gyroscopes. Thesystem 900 provides a calibration mount 998 for coupling a sensor 204 ina known, fixed position and orientation relative to the surgicalorientation device 172A. The calibration mount 998 is a docking devicethat positions the sensor 204 just prior to a step of eliminating anypotential source of accumulated error, e.g., zeroing a drift-sensitivesensor. FIG. 37-38 show that they system 900A can include two sensors204, one mounted to the registration jig 940 and one to the calibrationmount 998. These two sensors 204 can be identical or can be dedicatedfor their specific function. FIGS. 39 and 40 shows only one sensor 204.In this system, a single sensor 204 is used to gather landmark data andto work in combination with the impactor 300A to place an acetabularimplant.

FIGS. 41-43B illustrate various features for clamping structures to theplatform 908. In particular, these figures show fixation pin securementdevices 970 that are incorporated into the platform 908. The fixationpin securement devices 970 can have low profile to be out of the way ofother tools in the surgical field. FIG. 41-41A show one embodiment of apin securement device 970 that includes a compression member 972. Thecannula coupling device 912 can include a similar mechanism to clamp apin disposed through the cannula 924. The platform 908 includes a slotor plurality of slots formed on a surface thereof, e.g., on the topsurface. The slots 974 are larger in at least one direction than thecompression member 972 such that the compression member can fit in theslot and move to some extent therein. The compression member 972 has atapered channel 976. Movement of a tapered member 978 vertically in thetapered channel 976 shifts the compression member 972 to narrow a gap Gbetween the compression member 972 and a rigid feature of the platform.The gap G can be between a curved lateral surface of the compressionmember 972 and a curved surface of the platform 908.

In one method, a pin or other fixation member is advanced through thegap G and into the bone. The platform 908 is positioned on the fixationmember at an appropriate height and the pin securement device 970 isaffixed to the fixation member. The fixation member can be a Steinmannpin or other similar device. In one technique, the tapered member 978 isa threaded elongate body that is advanced along internal threads formedin the platform 908 until the tapered surface thereof acts on thetapered surface 976 to shift the compression member 972 laterally tonarrow the gap G. Further advancement of the tapered member 978 furthershifts the compression member 972 to enhanced securement of the fixationmember. The method can be repeated for a second pin, where one pinextends through the cannula 924 and one extends parallel to the cannula924, but off-set superiorly therefrom on the patient.

FIGS. 42-42B illustrate another approach to a fixation pin securementdevices 970A in which the fixation pin securement device comprises acompression member 972A pivotally mounted to the platform 908. FIG. 42Ashows two compression members 972A, each of which is mounted to pivotabout a pin or shaft 980. The securement device 970A on the left in FIG.42A corresponds to a configuration in which a fixation member can freelypass through a gap G in the mechanism. The securement device 970A on theright in FIG. 42A corresponds to a configuration in which the gap G isnarrowed and a fixation member disposed in the gap G will be securelyclamped and unable to move relative to the platform 908. A rigid surfaceof the platform 908 opposite the pivoting compression member 972 alongwith the compression member holds the fixation member in place.

In one method, pins or other fixation members are placed in the fixationpin securement device 970A and the cannula coupling device 912. In theillustrated embodiment, these devices can employ similar clampingmechanisms. Thereafter, screws 982 are advanced to cause the compressionmember 972 to pivot about the pin or shaft 980 from a first position inwhich the gap G provided between a clamping surface of the compressionmember 972A and a rigid surface of the platform 908 is larger to asecond position in which the gap G is smaller. The second position is aclamped position for the fixation member and will retain the platform inposition until the screw 982 is withdrawn enlarging the gap G.

FIGS. 43-43B illustrate another approach to a fixation pin securementdevices 970B in which the fixation pin securement device comprises acompression member 972B configured to clamp a plurality of segments ofan outside surface of a fixation member. The platform 908 includes aplurality of projections 984 extending upward from an upper surface ofthe platform. The projections preferably are threaded. Each projectionincludes a collet 986 or similar device disposed therein having an innerlumen sized to receive a fixation member. A plurality of slots extendsdownward from an upper surface of the collet 986 and an angled surface988 is disposed between top ends of each member defined between a pairof such slots. A corresponding angled surface 990 is provided on aninside of a cap 992. The cap 992 has internal threads that act on thethreads of the projection 984 to advance the angled surfaces 990 ontothe angled surfaces 988. Further advancement collapses the slots of thecollet 986 causing compression about the outer surface of the fixationmember. FIG. 43 shows that this approach can be used for the fixationpin securement devices 970B and/or for the cannula coupling device 912.

While the systems discussed above are well suited for specificapproaches, the system 900 can be adapted for a posterior approach orfor an anterior approach. This provides a great deal of flexibility tothe surgeon and only adds minimal additional components to a universalkit. The orientation of the axis of rotation A (see FIGS. 38 and 40)enhances the sensitivity of a system that incorporates accelerometersand other sensor drift insensitive components. The home point features968A, 968B enable the surgeon to obtain maximal accuracy by allowing theacquisition of position and orientation data for a number of anatomicallandmarks at close range to the home point position. This allows thesystem to initialize the sensors near the points to be acquired toenhance accuracy.

II. Hip Navigation Using Camera Tracking

FIG. 33 illustrates one embodiment of a system 800 that includesclose-range optical tracking capabilities. In this context “close range”is a broad term that means near the patient, such as any of in thesurgical field, directly above the pelvis but below the surgeon's head,within the boundaries of the surgical table, etc. This term is intendedto exclude systems where cameras are outside the surgical fields. Closerange greatly reduces or eliminates “line of sight” problems that plaguetraditional optical navigation.

In the illustrated embodiment, a jig system 804 is provided forconnecting to patient bone. The jig system 804 can include any of thefeatures of any of the jig systems discussed herein. For simplicity, thejig system is illustrated with that of FIG. 1, e.g., including thecannula 124 and the platform 136. A surgical orientation device 172A ismounted to the platform 136. The orientation device 172A can be similarto those hereinbefore described, but also includes one or more cameras812. Preferably the orientation device 172A includes two or more cameras812 to enable capture of binocular data. The cameras preferably aresmall cameras, for example the Aptina MT9T111, which is discussed athttp://www.aptina.com/products/soc/mt9t111d00stc/. The cones projectingfrom the lower side of the device 172A schematically represent thedirection of the field of view of the cameras 812.

This data can at least be used to determine the heading of and in somecases six degrees of freedom of a stylus 816. The stylus has a distalend 828 configured to touch landmarks as part of a landmark acquisitionmaneuver, as discussed above. A proximal (or other) portion 832 of thestylus 816 has an array of trackers 836 that can be tracked by thecameras 812 to provide orientation, position, heading, attitude, orother combinations of spatial characteristics of portions of the stylus816 or anatomy with which it is coupled.

The cameras 812 can operate without any additional sensor, such asinertial sensors. In some embodiments, the cameras 812 are used inconcert with inertial sensors to confirm or to improve accuracy of thesensors. For example, drift in a rate sensor, e.g., accumulated errors,can be monitored by comparing the output of the rate sensor with theviewed position from the cameras. The system can intervene if the sensoroutput drifts too much, for example, telling the user to reset the ratesensors.

Another optical device such as a laser or an IR emitter 814 can beprovided in the orientation device 172A. An IR emitter can be useful toilluminate the fiduciaries to make them more readily detectable by thecameras under the intense lighting in the surgical field.

Although these inventions have been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that this application extends beyond the specificallydisclosed embodiments to other alternative embodiments and/or uses ofthe invention and obvious modifications and equivalents thereof. Inaddition, while a number of variations of the inventions have been shownand described in detail, other modifications, which are within the scopeof the inventions, will be readily apparent to those of skill in the artbased upon this disclosure. It is also contemplated that variouscombinations or sub-combinations of the specific features and aspects ofthe embodiments may be made and still fall within the scope of theapplication. For example, the application contemplates the connectionhub alone or in combination with any of the other modules could comprisea separate aspect. Or, any one or a combination of the modules could bedirectly connected to an umbrella hub or overhead support to formanother separate aspect. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can becombined with or substituted for one another in order to form varyingmodes of the disclosed embodiments. Thus, it is intended that the scopeof the present invention herein disclosed should not be limited by theparticular disclosed embodiments described above, but should bedetermined only by a fair reading of the claims that follow.

Similarly, this method of disclosure, is not to be interpreted asreflecting an intention that any claim require more features than areexpressly recited in that claim. Rather, as the following claimsreflect, inventive aspects lie in a combination of fewer than allfeatures of any single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment.

What is claimed is:
 1. A method for performing a hip joint replacement,comprising: advancing a first portion of a jig into a portion of thepelvis; coupling at least one inertial sensor to the jig; moving asecond portion of the jig relative to the first portion to sequentiallytouch a plurality of anatomical landmarks; and placing a cup portion ofa replacement joint in the acetabulum by reference to a plane calculatedbased on data from the at least one inertial sensors.
 2. The method ofclaim 1, wherein the anatomical landmarks include a location on theilium of the pelvis at or adjacent to the acetabular rim.
 3. The methodof claim 1, wherein the landmarks include a location on one or both ofthe ischium and the pubis at or adjacent to the acetabular rim.
 4. Themethod of claim 1, further comprising moving the second portion of thejig to touch at least one anatomical landmark on a proximal femur of thepatient prior to separating the femur from the pelvis.
 5. The method ofclaim 1, further comprising moving the second portion of the jig totouch at least one anatomical landmark on a proximal femur of thepatient after connecting a ball of a replacement joint with a cup of thereplacement joint.
 6. The method of claim 1, further comprising couplinga first inertial sensor with the first portion of the jig and a secondinertial sensor with the second portion of the jig.
 7. The method ofclaim 6, wherein the first inertial sensor includes a user interface. 8.The method of claim 1, further recording an indication of lineardistance after touching the respective anatomical landmark.
 9. Themethod of claim 1, further comprising zeroing at least one inertialsensor shortly prior to at least one of the moving or placing steps. 10.The method of claim 9, wherein zeroing is performed not more than oneminute before at least one of the moving or placing steps.
 11. Themethod of claim 1, further comprising preparing the acetabulum with aninstrument the orientation of which is monitored by a tracking system.12. A method for performing a hip joint replacement, comprising:positioning a first hip joint of a patient on a surgical table and asecond hip joint off of the table such that an anterior pelvic plane isdisposed upright relative to the surgical table; coupling a jig with abone adjacent to a second hip joint, the jig comprising a moveableorientation guide having an inertial sensor coupled therewith; orientingthe orientation guide in a plane substantially parallel to a planecontaining an upper surface of the table; and recording the orientationof the inertial sensor as an indication of the orientation of theanterior pelvic plane; positioning a cup of an artificial hip joint inthe acetabulum with reference to the orientation of the anterior pelvicplane based on the orientation of the inertial sensor.
 13. The method ofclaim 12, further comprising mounting an inertial sensor and the cup ofthe artificial hip joint on an impactor and aligning the cup relative tothe acetabulum based on data from the inertial sensor coupled with thejig.
 14. The method of claim 13, further comprising removing theinertial sensor coupled with the orientation guide and coupling the sameinertial sensor with the impactor.
 15. The method of claim 13, furthercomprising preventing movement of the inertial sensor coupled with thejig and coupling a second inertial sensor with the impactor, data fromthe inertial sensor coupled with the jig enabling tracking of patientmovement.
 16. The method of claim 12, wherein the inertial sensorcoupled with the moveable orientation guide is configured as a tiltmeter.
 17. The method of claim 16, wherein the inertial sensor operatessolely based on sensors unaffected by drift errors.
 18. The method ofclaim 12, wherein the indication of the orientation of the anteriorpelvic plane is a first indication of the orientation and furthercomprising establishing a second indication of the orientation bycontacting a probe feature of the orientation guide with a plurality ofanatomical landmarks disposed about the acetabulum, the points ofcontact being used to calculate a proxy acetabular plane.
 19. The methodof claim 18, further comprising positioning the cup based on both thefirst indication of the orientation and the second indication of theorientation.